Les systèmes d'irrigation des rizières d'Afrique vus du ciel

La technologie des drones procure aux agriculteurs un moyen économique de planifier l'infrastructure. Au Nigeria, elle a permis d'accélérer la planification, la conception et la construction des systèmes d'irrigation des rizières.  

À mesure que le drone, appelés dans le monde anglophone « véhicules aériens sans pilote (UAV) », réapparaît au loin et perd de l'altitude pour se poser, Richard, le chauffeur de l'équipe de chercheurs qui s'est porté volontaire pour apporter son soutien à la mission, court plein d'enthousiasme vers l'avion sans pilote. « Bienvenue ! » s'écrie-t-il en exultant, à la fois en anglais et en haoussa, la langue parlée dans le nord du Nigeria.

L'équipe growmoreX de la société londonienne GMX Consultancy, gestionnaire d'un service applicatif agricole fondé sur les drones, était présente au Nigeria afin de réaliser une étude préalable au développement d'une exploitation rizicole irriguée de 3 000 hectares. L'exploitation occupera un terrain acquis via un bail à long terme signé avec l'administration publique locale chargée de l'irrigation. L'objectif du projet était d'étudier et de cartographier 7 500 hectares afin de préparer la planification et la construction de l'infrastructure d'irrigation des rizières.

Un aéronef piloté aurait coûté une fortune. La technologie des drones était une alternative bien moins coûteuse. Le site étudié dans le cadre du projet était une région à faible densité de population située environ à 75 kilomètres de la ville de New Bussa. Cette région se caractérise par un accès limité aux routes, à l'électricité, à l'eau potable ainsi qu'à d'autres équipements collectifs. La population y vit principalement de petites exploitations agricoles. Les habitants cultivent tous les ans au cours de la saison des pluies du sorgho, du riz et des haricots. Les tomates poussent pendant la saison sèche, grâce à l'irrigation par pompage.

Le premier vol

Un drone à voilure fixe importé directement des États-Unis a été utilisé pour le premier vol. La journée d'assemblage a donné le temps à l'équipe de résoudre les petits problèmes techniques et de comprendre comment utiliser sa fonction de planification automatique de mission.

Une fois tous les contrôles effectués, l'équipe a réglé le système de navigation du drone sur le mode « automatique ». L'hélice du drone s'est mise à tourner et celui-ci a pris son envol, sous les yeux émerveillés d'une foule qui s'était rassemblée pour observer le premier vol. La mission démarrait.

Bien qu'il ait effectué un bon décollage, le drone commença soudain à s'éloigner au lieu de débuter sa mission préprogrammée, probablement en raison de la direction du vent. L'équipe perdit la communication de télémétrie avec le drone et pensa que le drone s'était écrasé.

Mais soudain, la connexion radio avec le drone se rétablit et il entama sa mission de cartographie automatique. Il ne lui fallut que quelques minutes pour atteindre l'altitude de 150 mètres, considérée comme optimale pour son travail d'étude. Une fois arrivé à cette altitude, il se mit à voler selon une trajectoire spécifique, prenant automatiquement des photos pendant son vol.

Une planification précoce

L'appareil photographique fut contrôlé dès l'arrivée du drone sur le sol. Les photos semblaient nettes et de bonne qualité. Il y en avait beaucoup : au cours du vol de 55 minutes, le drone avait pris des photos superposées de quelque 300 hectares.

Le drone pouvait voler environ quatre heures par jour lorsque le soleil projetait le moins d'ombre possible. Dès lors, l'équipe put cartographier environ 1 000 hectares en une seule journée. Le processus est particulièrement rapide, surtout si l'on tient compte du terrain, des conditions de travail difficiles et des températures élevées. On estime qu'il aurait fallu une vingtaine de jours à un géomètre professionnel travaillant à pied pour couvrir la même surface.

Toutefois, faire appel à un drone nécessite de s'y prendre à l'avance. Les chercheurs se sont d'abord assurés qu'aucun règlement spécifique n'empêchait l'équipe d'utiliser ce type d’appareil. L'émir local, le chef du village, ainsi que les responsables d'un aéroport militaire situé à quelque 100 kilomètres du site étudié avaient été informés du projet. Les autorités locales avaient heureusement accueilli favorablement la nouvelle technologie. Une seule condition avait été imposée : l'émir avait insisté pour que son village soit survolé afin que sa population puisse observer le drone et les photos qu'il prendrait.

Le résultat fut inattendu. Pour la première fois, l'équipe a pu établir le nombre exact de maisons et d'habitations dans le village, permettant ainsi aux chercheurs d'effectuer une estimation bien plus précise de sa population. Cette information sera très utile, car l'équipe chargée de l'étude prévoit d'engager de la main-d'œuvre locale pour construire l'exploitation rizicole et la gérer.

Une hypothèse remise en cause

Aussi magnifique qu'ait été le survol du village, le principal objectif était la planification de l'infrastructure d'irrigation de la rizière. En se basant sur les premières études, les chercheurs devaient créer une carte à l'échelle 1:2 000 (1 centimètre de la carte représente 20 mètres). L'objectif de cette carte était que l'équipe prenne des décisions éclairées concernant la meilleure disposition des champs ainsi que des systèmes d'irrigation et de drainage.

En se fondant sur les informations limitées rassemblées à l'issue de visites précédentes du site, l'hypothèse était qu'il serait possible de disposer les rizières sous forme de vastes bassins rectangulaires. Il aurait fallu d'énormes machines de terrassement et du matériel agricole important pour construire et cultiver ces bassins. Les champs destinés à la culture du riz nécessitent une gestion prudente de l'eau car le niveau de l'eau influence la distribution des mauvaises herbes et des nutriments. Cela signifiait que tous les 100 mètres, 50 cm de terre devaient être éliminés en haut du champ afin de surélever sa partie inférieure au cours du processus de nivellement.

Toutefois, l'étude réalisée par le drone a infirmé cette hypothèse. Même s'il était vrai que certaines parties du site concerné étaient plates, la plus grande partie du terrain était vallonnée.

En raison du terrain en pente et de la finesse de la couche supérieure du sol, l'équipe de chercheurs a dû radicalement modifier son hypothèse et oublier la conception en vastes bassins rectangulaires pour opter pour de longs champs étroits qui suivraient les ondulations du terrain. Ce changement impliquait également une conception très différente du système d'irrigation.

Éviter des frais inutiles

À l'aide des données obtenues grâce à la technologie des drones, les planificateurs agricoles peuvent maintenant éviter plus facilement la mauvaise planification de l'infrastructure. Cette information facilite également l'organisation d'un approvisionnement adéquat en termes de matériel, ce qui permet d'éviter les gros investissements de départ inutiles pouvant mener un projet à l'échec.

L'eau est le facteur essentiel en matière d'autosuffisance rizicole en Afrique, où la culture du riz est principalement pluviale. Le manque d'infrastructures d'irrigation constitue un obstacle majeur à l'augmentation de la production rizicole sur le continent. La plupart des systèmes existants sont mal conçus, mal construits et mal entretenus.

Une bonne nouvelle : la technologie des drones peut accélérer la planification, la conception et la construction de l'infrastructure d'irrigation africaine. Comme ce projet l'a démontré, la technologie des drones pourrait offrir aux agriculteurs un moyen économique de planifier cette infrastructure.

Mais ce n'est pas tout. Après l'étape de planification, les drones pourraient être utiles aux exploitants en vue d'estimer avec plus de précision la quantité de fertilisants et de matériaux de plantation nécessaires pendant la période de végétation. Une fois les cultures plantées, des drones équipés de capteurs spéciaux peuvent surveiller leur croissance.

Avec l'aide des drones agricoles, l'Afrique peut se propulser directement à l'ère de l'agriculture de précision en pleine expansion, tout comme les entreprises africaines de mobilophonie ont court-circuité l'infrastructure traditionnelle des lignes fixes pour créer un système innovant de financement mobile.

À propos de l'auteur :

Quan Le (quan.le@gmx.com) est le directeur général de GMX Agri (www.gmxconsulting.co.uk), une entreprise de conseil, de développement et d'opération axée sur l'agriculture africaine.

Source:

Vous pouvez commander une version imprimée ou télécharger une version PDF de ce numéro en suivant ce lien.

Une sélection d'articles sont proposés sur le portail web du magazine : http://ictupdate.cta.int/fr, où vous pouvez vous abonner à la publication gratuitement.

A bird’s eye view on Africa’s rice irrigation systems

Drone technology provides agriculturists with a cost-effective method of infrastructure planning. In Nigeria it has accelerated the planning, design and construction of rice irrigation systems.

As the drone reappeared in the sky and lowered its altitude in an attempt to land, the research team’s driver Richard, who had been volunteering to help out with the mission, ran towards the unpiloted plane in jubilation. ‘You’re welcome!’ he said enthusiastically in both English and Hausa, the language that is spoken in northern Nigeria.

The growmoreX team of the London based company GMX Consultancy, which runs a drone-based farming application service, was in Nigeria to do a preliminary assessment for the development of a 3,000 hectares irrigated rice farm. The farm will be built on land that was acquired in a long term lease from the local government’s irrigation authority. The aim of the project was to survey and map a total of 7,500 hectares in preparation of planning and building the irrigation infrastructure for the rice fields.

Although a manned aircraft could have done the job, it also would have cost a fortune. The alternative is unmanned aerial vehicle (UAV) technology. The project site was in a sparsely populated area, located approximately 75 kilometres from the town New Bussa, some 700 kilometres away from the capital Abidjan with limited access to roads, electricity, clean water, and other amenities. Local livelihoods here are mainly based on small-scale agriculture. Crops are grown annually during the rainy season, and include sorghum, rice and beans. Tomatoes are grown during the dry season using pump-fed irrigation.

First flight

A fixed-wing UAV, which was imported directly from the US with assistance from a local project partner, was used for the first flight. It took a day to assemble it. That gave the team time to sort out technical hiccups and figure out how to use its automatic mission planning function. The activity attracted attention from local villagers, who had already been informed about the forthcoming agribusiness development.

When all the checks were completed, the team set the UAV’s navigation system to ‘automatic’. Then the UAV’s propeller was turning and it was launched into the air, witnessed by a crowd of people who had gathered to watch the first flight. The mission had begun.

Although the UAV had made it into the air, it suddenly began to fly away instead of starting its pre-programmed mission – likely due to the direction of the wind. The team lost telemetry communication with the drone, and it was thought that the UAV had crashed.

Suddenly, the radio established a connection with the UAV again, and it finally began its automatic mapping mission. It took the UAV only a few minutes to reach the optimal surveying altitude of 150 metres above ground level. Once at this altitude, it began to fly in a specific pattern, shooting images automatically as it went.

Advance planning

After the UAV landed safely the camera was checked immediately. The photos looked sharp and beautiful. There were a lot of them: during the 55-minute flight, the drone took overlapping photos of nearly 300 hectares of land.

The UAV was able to fly for roughly four hours a day when the sun cast the fewest shadows. This meant that the team was able to map about 1,000 hectares in a single day. That is fast, especially if the harsh terrain and working conditions with high temperatures are considered. Estimations assume that it would have taken a professional surveyor working on foot about twenty days to cover the same area.

To operate an UAV requires advance planning. The researchers made sure no specific regulations barred the team from using the UAV. The local Emir, the village chief and a military airport located about 100 kilometres from the project site were informed of the plans to make use of an UAV. Fortunately, the local authorities welcomed the new technology. There was only one condition: the Emir insisted that we do a flyover of his village, so that his people could see both the drone and the pictures it would take.

The village flyover had an unexpected result. For the first time the team could establish exactly how many houses and dwellings there are in the village, thus enabling researchers to make a much better estimation of its population. This information will be very useful, because the research team is planning to hire local labour to build the rice farm and to run it.

The hypothesis was proved wrong

Wonderful as the village flyover was, the main objective was to begin planning the rice farm’s irrigation infrastructure. For the preliminary investigation, the researchers needed to create a map at a scale of 1:2,000 (1 centimetre on the map represents 20 metres). With such a map the research team could make informed decisions on the best layout of the paddy fields, the irrigation and drainage systems.

Based on the limited information from previous visits to the site, it was hypothesised that it would have been able to lay out the rice fields as large, rectangular basins. Large earth moving and farming machinery would have been needed to build and cultivate those basins. Paddy fields for rice cultivation need careful water management as water levels impact weed and nutrient distribution. This meant that for every 100 metres, half a metre of soil at the top of the field had to be removed to raise its lower end during the levelling process.

However, the drone survey proved the hypothesis wrong. Although it was certainly true that parts of the project site were flat, most of the terrain was an undulating landscape.
The sloping terrain combined with a thin top soil layer led the team of researchers to radically change their designed hypothesis, away from large rectangular basins and towards long, narrow fields that would follow the terrain. But this change also meant that a very different irrigation system design was necessary.

Avoiding unnecessary costs

By using data required from UAV technology, agricultural planners can now easier avoid incorrect infrastructural planning. This information also makes it easier to organise the right procurement of machinery, avoiding unnecessary large upfront investments that can break a project if they are improperly planned.

Water is the deciding factor in Africa’s rice self-sufficiency. Most rice cultivation is rain-fed in Africa. The lack of irrigation infrastructure is a major obstacle to increase rice production on the continent. Most of the existing systems are poorly designed, built, and maintained.

The good news is that UAV technology can potentially accelerate the planning, design and construction of Africa's irrigation infrastructure. As this project has shown, UAV technology could provide agriculturists with a cost-effective method of irrigation infrastructure planning.

And that is not all. After the farm planning stage, UAVs could be useful for farmers to estimate more accurately how much fertilizer and planting materials they will need during the growing season. Once crops have been planted, UAVs equipped with special sensors can monitor their growth.

With the help of agricultural UAVs, Africa can leapfrog into the quickly-advancing area of precision agriculture – just as African mobile phone companies bypassed traditional fixed line infrastructure to create an innovative mobile finance system.

About the author:

Quan Le (quan.le@gmx.com) is managing director of GMX Agri, an Africa-focused agriculture adviser, developer and operator. The firm recently launched growmoreX, an UAV-based farming application service. It collaborates with UAV operators in Africa.

Source:

Republished with permission from ICT Update, issue 82, April 2016

Les cinq étapes de la création d’une carte au moyen de petits drones

Auparavant, on représentait tous les éléments d’une carte par des symboles dont les caractéristiques spatiales (emplacement, taille, forme) pouvaient être définies mathématiquement dans un système référentiel de coordonnées. On appelait « données vectorielles » les informations spatiales sous-jacentes aux éléments représentés de cette manière. En revanche, depuis l’apparition de la photographie aérienne, on peut désormais également produire des cartes avec des cellules de quadrillage (ou pixels) à chacune desquelles on assigne des valeurs de couleur normalisées, exactement comme pour une image numérique. On appelle « données raster » (ou matricielles) les données utilisées pour produire ce type de carte. Les cartes élaborées à partir des capteurs embarqués à bord des véhicules aériens sans pilote (VASP) ou drones sont dites « sous format matriciel ».

Une carte, au sens traditionnel du terme, doit au minimum répondre aux conditions suivantes : elle doit comporter une échelle et une flèche indiquant le nord, et elle doit offrir un grand degré de cohérence dans la précision des données. De nos jours, au lieu d’utiliser une échelle donnée pour obtenir la résolution souhaitée, les experts utilisent la résolution au sol (Ground sample distance, GSD). Cela représente la largeur et la longueur de la zone couverte au sol par un seul pixel de la mosaïque de capteurs de la caméra. La précision de la carte est donc intimement liée à la GSD. Pour une GSD fixée à 20 centimètres, il ne sera pas possible d’obtenir une mesure des distances entre des points perceptibles au sol plus précise que 20 cm.

Cinq étapes sont nécessaires pour créer une carte au moyen de drones de petite taille :

Étape 1. Conception de la carte et des plans de vol

Afin de s’assurer que la carte sera bien adaptée aux objectifs poursuivis, il importe de déterminer dès le début du processus le type de capteur(s) à utiliser (de lumière visible, de lumière infrarouge, multispectral ou hyperspectral). Une fois le type de capteur déterminé, il faut fixer la GSD adéquate. Plus la résolution au sol diminue et plus la résolution (et la précision) de la carte sera élevée.

Pour évaluer la résolution au sol souhaitée avec un appareil donné, il faut calculer l’altitude de vol correspondante, qui sera fonction de la résolution du ou des capteur(s) et de la distance focale de l’optique de la caméra. La création de cartes à partir d’images doit de plus garantir un recouvrement minimum des photos (exprimé en pourcentage). Pour satisfaire aux exigences en matière de recouvrement, il convient de calculer les intervalles auxquels l’appareil doit se déclencher, ainsi que l’espacement des bandes adjacentes au moyen des dimensions de l’empreinte au sol d’une image.

La Figure 1 illustre le rapport entre, d’une part, la taille et la résolution du capteur ainsi que la distance focale et l’altitude de vol et, d’autre part, la résolution au sol (GSD) et les espacements entre les déclenchements et entre les bandes.

Figure 1 : Paramètres du plan de vol (en mètres)

Par exemple, pour une GSD fixée à 12 millimètres, l’altitude de vol est de 50 mètres, l’appareil doit se déclencher tous les 9,8 mètres dans la bande de vol, et les bandes de vol doivent être espacées de 22 mètres.  
Une fois ces paramètres calculés, on peut mettre au point un plan de vol pour couvrir la zone d’intérêt. Il existe de nombreux outils de conception de plans de vol (gratuits ou payants) pour générer des plans de vol et des plans de tâches numériques de manière quasi automatique qui pourront ensuite être téléchargés sur le drone qui les exécutera alors automatiquement.

Étape 2. Acquisition des images

Afin de permettre l’orientation et la position absolues de la future carte, c’est-à-dire pour géo-référencer cette carte, il est nécessaire de placer sur le terrain des balises de taille et de forme adéquates : ces « Points de contrôle au sol » (PCS) doivent pouvoir être formellement identifiés sur l’imagerie aérienne, et leurs coordonnées dans le système de cartographie de référence souhaité seront mesurées par des méthodes de géomètres.

Dès que les balises PCS sont en place, le plan de vol peut être téléchargé sur le drone pour y être exécuté. Pour un fonctionnement sûr, il convient de procéder à des vérifications de vol et à l’évaluation du terrain avant le lancement du drone. À l’atterrissage, on télécharge le journal de bord et les images aériennes du drone vers un ordinateur portable ou un périphérique de stockage avant de procéder au traitement des images.

Étape 3. Traitement des images 

On associe volontiers la technologie des drones à la production de cartes en haute résolution, mais, sans la technologie de la Structure from Motion (SfM), la révolution cartographique que nous connaissons n’aurait jamais pu avoir lieu. Le degré d’automatisation extrêmement élevé qui caractérise cette technique de cartographie est essentiel pour la démocratisation de la production de cartes.

La première étape de la SfM consiste à aligner les caméras, processus accéléré par l’introduction des positions approximatives des caméras telles qu’enregistrées par le contrôleur de vol du drone. Ces positions approximatives sont également utilisées pour géo-référencer les positions des caméras, ainsi que tous les produits en aval générés par le processus de SfM. Lorsque des PCS (ainsi que leurs coordonnées terrestres) sont nécessaires pour un géoréférencement plus précis, leurs coordonnées-image doivent être visibles dans chaque visuel dans lequel ils apparaissent. Cette étape est généralement la seule intervention manuelle de la procédure de SfM. Dès qu’un modèle de terrain et un atlas de textures ont été produits, on peut générer différents produits géo-spatiaux. En règle générale, sur un ordinateur portable, on peut traiter quelque 500 images de 20MP (couvrant entre 5 et 10 hectares à une résolution au sol entre 10 et 20 millimètres) de grande qualité en l’espace de 24 heures environ.

Étape 4. Préparation et visualisation des produits géo-spatiaux

Une fois le processus de SfM achevé, on peut extraire différents produits géo-spatiaux. Pour une représentation en deux dimensions du terrain, on génère une orthophotographie sur le référentiel et la projection souhaités. On obtient alors une carte raster géo-référencée sans distorsion. Pour ajouter la troisième dimension, on peut générer un modèle altimétrique numérique (MAN) sous format matriciel ou vectoriel. L’association des produits susmentionnés permet des visualisations en 3D extrêmement réalistes, ainsi que des analyses plus ou moins automatiques relatives à la santé de la végétation, la détection de bâtiments, l’évaluation des sols sous l’angle du drainage et de l’irrigation, ou encore au calcul des volumes et de la hauteur des cultures.

Étape 5. L’extraction d’informations essentielles 

Des cartes matricielles véhiculent une quantité impressionnante d’informations, mais la diffusion des volumes de données très importants qu’elles contiennent occuperait une quantité considérable de bande passante. De nombreux logiciels de représentation graphique sont incapables de gérer de tels volumes. Il est donc impératif d’extraire des volumes de données les éléments essentiels pour toute analyse spécifique.

Cette opération est réalisée grâce à l’arpentage virtuel, un processus permettant à l’« arpenteur » de parcourir sans effort le terrain virtuel tout en procédant à des mesures, comme s’il se trouvait sur le terrain. Toutes les données capturées ainsi par l’« arpenteur virtuel » sont sauvegardées sous format vectoriel (format le plus efficace) puis exportées vers un logiciel DAO ou un système d’information géographique (SIG). La possibilité de se livrer à des travaux de topographie virtuels permet d’améliorer considérablement les performances et de réduire les coûts liés aux travaux de cartographie et de topographie. Le travail sur le terrain ne prend plus que quelques heures contre plusieurs semaines auparavant, voire plusieurs mois.

Autres progrès liés à la cartographie par drones

Notons que la cartographie SfM sans PCS est également possible : il suffit alors de connecter un récepteur miniaturisé de système mondial de navigation par satellite (GNSS) à double fréquence à la caméra pour enregistrer le moment précis de chaque déclenchement de l’appareil. De cette manière, les positions de déclenchement peuvent être déterminées de manière très précise, au centimètre près. Certains soutiennent que cette manière de procéder permet de faire l’impasse sur les PCS. De toute évidence, cette nouvelle approche devra faire l’objet de recherches plus approfondies avant de pouvoir convaincre les professionnels de la cartographie.

Enfin, l’émergence de scanners Lidar toujours plus légers constitue un autre progrès important. Le Lidar présente l’avantage unique de pouvoir pénétrer à travers la végétation, ce que n’arrive pas à faire la SfM.

Grâce à ces étapes et ces développements, les cartes numériques peuvent désormais être créées et analysées.

À propos de l’auteur :

Walter Volkmann (walter@unirove.com) préside Micro Aerial Projects L.L.C., une entreprise officielle de mesures géodésiques et cadastrales, spécialisée dans les solutions géo-spatiales.

Source:

Vous pouvez commander une version imprimée ou télécharger une version PDF de ce numéro en suivant ce lien : http://bit.ly/uav4ag-FR

Une sélection d'articles sont proposés sur le portail web du magazine : http://ictupdate.cta.int/fr, où vous pouvez vous abonner à la publication gratuitement.

Five steps of making a map with small drones

Traditionally all features on a map were represented in the form of symbols whose spatial characteristics, like location, size and shape, could be mathematically defined in a spatial reference system. The underlying spatial information of features depicted in this way is referred to as vector data. Since the arrival of aerial photography, however, maps could also be made with contiguous cells, called pixels, to each of which normalised colour values are attached, just like a digital image. The data used to make a map in this way is referred to as raster data. The maps derived directly from unmanned aerial vehicles (UAV)-carried sensors are in raster form.

In the classical sense, a map has to satisfy at least the following basic conditions: it has to have a scale, a north arrow and be of uniform accuracy across the mapping domain. The scale on printed maps determined its resolution as well as its accuracy. In the digital age the scale of a map can be changed by simply scrolling the wheel of your mouse. Instead of using scale to achieve desired resolution, analysts nowadays make use of the Ground Sampling Distance (GSD). The GSD represents the width and length of the area covered on the ground by one pixel on the sensor array of the camera. For any given camera, the GSD is thus a function of how high above the ground the camera is located. The accuracy of the map is in turn intrinsically linked to the GSD. For a GSD of 20 centimetres it is not possible to measure distances between discernible features more accurately than 20 centimetres.

The small drone mapping workflow can be divided into five steps.

Step 1. Map design and flight planning

To ensure that the map is made “fit for purpose” it is important to decide from the outset which type of sensor(s) (visible light, infrared, multispectral, hyperspectral) will be needed. Once the appropriate sensor has been identified, the appropriate GSD has to be determined. The smaller the GSD, the higher the resolution (and accuracy) of the map will be.

To achieve the desired GSD with a given camera the corresponding flying height has to be computed. This is a function of the sensor resolution and the focal length of the lens of the camera. Moreover, making maps from images requires the so-called “stereo effect” which is brought about by image overlaps. Overlaps along the flight direction and between adjacent strips are expressed in percentages. Using the footprint dimensions of an image on the ground, the intervals at which the camera must expose and the spacing of adjacent lines which will satisfy the overlap conditions must be computed.

Figure 1 illustrates the relationship between camera sensor size and resolution, focal length and flying height on the one hand and GSD, photo and line spacing on the other.

Figure 1: Flight Planning Parameters (in units of meters)

For example, a GSD of 12 millimetres requires a flying height of 50 metres, the camera must be exposed every 9.8 metres along the flight line and flight lines must have a spacing of 22 metres.
With these parameters a flight plan can be compiled to cover the area of interest. There are many flight planning tools (open source as well as proprietary) available to more or less automatically generate digital flight and task plans which can be uploaded to the drone for automatic execution.

Step 2. Image acquisition

To provide the resulting map with absolute orientation and location, in other words to geo-reference it, it is necessary to place suitably sized and shaped targets on the terrain. These targets, known as Ground Control Points (GCPs) must be positively identifiable in the aerial imagery and their coordinates in the desired mapping reference system have to be established by survey. Obviously the targets have to be in place during the time of aerial image capture, however, they can be surveyed before or after image acquisition.

Once the GCP targets are in place, the flight plan can be uploaded to the drone for automatic execution. To ensure a safe operation, launching the drone should be preceded with flight checks and terrain evaluation. Upon landing the flight logs of the drone and the aerial images are downloaded to a laptop or storage device for processing.

Step 3. Image processing 

Drone technology is predominantly associated with high resolution mapping, but without the powerful Structure from Motion (SfM) technique we would not be experiencing the current mapping revolution. The very high degree of automation in this robust mapping technique is key in the democratization of map making.

The first step in the SfM workflow is the alignment of the cameras. This process can be accelerated by introducing the approximate camera exposure positions as recorded by the flight controller of the drone. These approximate camera positions are also used to approximately geo-reference the positions of the camera positions as well as all subsequent products generated by the SfM process. When GCPs (with their terrestrially determined coordinates) are needed for more precise geo-referencing, their image coordinates have to be observed in each image on which they appear. This is commonly the only manual intervention in the SfM process. Once a terrain model and a texture atlas have been derived, various geo-spatial products can be generated. As a rough rule of thumb some 500 20MP images (covering some 5 to 10 hectares at 10 to 20 millimetres GSD) can be processed at high quality in a matter of 24 hours or less on a gaming laptop.

Step 4. Preparation and visualisation of geo-spatial products

Once the SfM process has been completed various geo-spatial products can be extracted. For a two-dimensional depiction of the terrain an ortho photo is generated on a desired mapping datum and projection. This is a geo-referenced, distortion free raster map (as opposed to a distorted mosaic of “stitched” images). To add the third dimension a digital elevation model (DEM) either in raster or in vector form can be generated. Combining the above products allows for highly realistic 3D visualisations as well as more or less automated analyses such as vegetation health, building detections, terrain evaluations with regard to drainage and irrigation, volume calculations and crop heights, to mention a few.

Step 5. The extraction of essential information 

While raster maps such as high resolution ortho photos with underlying DEMs can convey a tremendous amount of information, they do so at the expense of very large data volumes which require considerable bandwidth for dissemination. Many graphic information systems, such as Computer Aided Drafting (CAD) programmes simply cannot handle these volumes. It is thus necessary to extract from the mass data volumes those elements that are essential for a specific analysis.

This is done by means of virtual surveying, a process which enables the “surveyor” to effortlessly navigate on and over the virtual terrain while performing measurements as if he were in the field. All data captured by the “virtual surveyor” in this fashion is saved in the much more efficient vector format and subsequently exported to CAD or Geographic Information Systems (GIS). The ability to do surveys virtually brings about enormous performance improvements and cost savings to mapping and surveying, typically reducing field work from weeks or months to a few hours.

Other developments related to drone mapping

It should be mentioned that SfM mapping without the use of GCP is also possible. This is accomplished by connecting a miniaturised dual frequency global navigation satellite system (GNSS) receiver to the camera to record the exact time of each exposure. In this way the camera exposure positions can be determined accurately to a few centimetres, thus it is argued, obviating the need for GCP. More research is needed before this approach can overcome the scepticism of many mapping professionals.

Finally, the emergence of ever lighter Lidar scanners is another important development. Lidar has the distinct advantage of penetrating vegetation, something which SfM fails to do.

With these steps and developments in mind digital maps can be created and analysed.

About the author:

Walter Volkmann (walter@unirove.com) is president of Micro Aerial Projects L.L.C., a geodetic and cadastral Surveyor, and geo-spatial solutions specialist.

Source:

Republished with permission from ICT Update, issue 82, April 2016

Follow @UAV4Ag on Twitter

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Making sense of drone regulations

Authorities demand regulation for and supervision of the increasing use of drones, because of privacy, safety and security issues. Drone operators must be aware of this. 

While unmanned aerial vehicles (UAV) – also known as drones – are indisputably useful for civilians, the technology has an increasing public relations problem. For example, UK pilots were calling for research into what would happen if a UAV hit an airliner, after 23 near-misses around UK airports in six months during 2015. In Japan, UAVs equipped with a net have been developed to capture rogue UAVs that might threaten disruptions along flight paths. And the Dutch police are experimenting with trained eagles to take unwanted UAVs out of the sky.

Some people are wary of drones due to the technology's association with lethal military technology. Others have seen recent news reports describing the reckless and indiscreet use of UAVs by civilians, from paparazzi drones to unauthorized UAVs flights over tourist hot-spots. These incidents have made governments and citizens around the world raise serious concerns about leaving the technology unregulated.

Image: Walter Volkmann

PhotoThe debate about UAV regulation also concerns developing countries. Some nations, like South Africa, have already implemented regulations on the use of the technology by civilians, while others, like Kenya, have banned the use of UAVs without explicit permission from authorities. Several small island developing states in the Pacific have adopted the regulations formulated by their bigger, more developed neighbours. That is the case for Samoa and Tonga, for example, who follow the UAV laws of New Zealand. Still, many developing countries have no provision at all when it comes to the use of this technology by civilians.

Why rules and standards are necessary

One of the fundamental prerequisites for the use of small UAVs in public airspace is the existence of harmonised rules, in particular for UAV operators. These rules should pertain to safety and training, facilitate cross-country recognition of aircraft and pilot certification. Furthermore, such regulations should be combined with appropriate provisions for the protection of public privacy, data protection, liability and insurance. UAV rules also need standards that apply to both private and commercial use, covering issues such as the identification of types of small UAVs, and development of technologies that can prevent hackers or third parties from taking control of the devices while they are in the air. Clear and concise guidance material, customs procedures, simplified regulations, and readily available online forms and information products, like maps that show where it is allowed or not to use UAVs, could all help to succeed in reducing risks for operators.

The increasing commercial exploitation of smaller drones will require further, specific adjustments, such as limitations on third-party liability, the introduction of UAV weight categories below 500 kilograms, and adjustments to the risk levels that are associated with the flight characteristics of very small UAVs. Some concerns with UAVs are not new: the protection of fundamental civilian rights, such as the privacy of images and data, was already an issue with the use of manned aircraft and helicopters. In this context UAVs represent an increase in the scale of aerial data collection – a new challenge when it comes to strengthening and managing the legal protection of privacy rights and both personal and business data.

The international discussion about regulation of the commercial application of UAVs formally began in 2007 with the creation of an unmanned aerial system study group within the International Civil Aviation Organisation (ICAO). The study group brought to the table several member states and aviation management organizations. In 2011 the study group produced a circular 328, followed in 2015 by a manual on unmanned aircraft systems and proposed amendments to national civil aviation laws.

ICAO's current coordination efforts in the international arena focus almost exclusively on the large remotely-piloted aircrafts used for trans-boundary missions and not on the smaller UAVs. However, much of the material that was prepared by the study group is useful to develop country-specific and regionally relevant regulations for small UAVs under 500 kilograms and with visual line-of-sight operations, as Leslie Cary, who manages ICAO’s programme on drones, said at the Remotely Piloted Aircraft Systems Symposium in March 2015.

The European Aviation Safety Agency (EASA) has been tasked by the European Commission to develop a regulatory framework for drone operations and proposals for the regulation of civil, low-risk drone operations. In achieving this, EASA is working closely with the Joint Authorities for Rulemaking of Unmanned Systems (JARUS), which is producing guidelines that should serve the UAV governance of the national airspaces.

Regulations in ACP countries

Research led by the Technical Centre for Agricultural and Rural Cooperation (CTA) recently examined the current state of drone-related regulations in the African, Caribbean and Pacific (ACP) group of states. It revealed several distinct categories of responses to the drone issue. Indeed, ICAO member states use the organisation's standards and recommended practices and other guidance material to develop their own regulations.

South Africa in particular has implemented and now enforces a comprehensive set of legally-bound rules governing UAVs, placing it among the small group of nations that have working regulations. Others, like Senegal and Kenya, have banned the civilian use of drones or specific airborne tools, such as cameras, although they have amended their aviation laws with drone-related provisions developed by ICAO. Others, like Chad and Gabon, still left notes in their newly updated aviation laws stating that international norms still need to be established on specifics such as certification, licensing and aircraft types. Others have created a variety of forms, guides and information products, and sometimes have simply adopted the UAV rules of another country, without any official amendments to their aviation laws.

In emergency situations, like post cyclone Vanuatu, drones have been used on Efate and Tanna islands for reconnaissance and damage assessment purposes with the endorsement of the government, but in the absence of a legal framework and specific rules. Thus, it appears that the question is no longer whether, but how and when the integration of UAVs into existing forms of aviation will take place. When rules are unclear, professional small UAV operators working in agriculture or natural resource management should use common sense and follow diligence: have an operator permit, documentation and registration for the aircraft and the instrument used, and seek approval from local authorities. Ideally they also should seek approval from customs and national transport agencies.  

Emerging UAV expertise

Tackling safety and privacy issues together with the adoption of harmonised relevant regulation will play a crucial role in the public acceptance of civilian drone technology, and the role of ICAO and JARUS is instrumental in developing the appropriate standards and recommended practices. Regional coordination efforts could spur further harmonisation of national operating rules, licences and certification between neighbouring countries. By doing this they could help the spread of commercial applications and facilitate the growth of regional enterprises and expertise on UAV technology.

ACP countries looking to regulate the technology should consult with professional operators and users of drones to ensure that UAVs’ user cases are well defined and their authorisation streamlined for the relevant activities within the individual countries.

About the Author:

Cédric Jeanneret (cedricj@gmail.com) is a freelance geographer. Cédric is particularly interested in capturing and analysing geographic information to map and learn about the diffusion of innovations and adoption of technology in socio-ecological systems.

Source:

Republished with consent from ICT Update, issue 82, April 2016

Related links:

• Website of the Joint Authorities for Rulemaking on Unmanned Systems (JARUS).
• ICAO study of legal issues relating to remotely piloted aircraft (2015):
•  Webpage of the South Africa Civil Aviation Authority on UAVs

Follow @UAV4Ag on Twitter

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Documenting illegal land occupancy using drones

Unmanned aerial vehicles have the potential to empower indigenous communities to become equal partners in the efforts to safeguard their territories and natural resources. 

Throughout the Americas, indigenous forest communities’ territories face intensifying threats, as global demand increases for land and forest resources. Non-indigenous settlers and loggers illegally enter indigenous territories to poach valuable timber or to burn and clear large swaths of forest.  Emerging technologies, such as unmanned aerial vehicles (UAVs) – also known as drones – offer an unprecedented opportunity to empower communities to defend their territories and natural resources. UAV technology allows them to monitor their land in real time, obtain visual evidence of any trespass, and make claims based on this evidence.

Some of Panama’s indigenous communities already make use of UAVs to protect the rainforest. Nearly 70% of Panama’s remaining intact rainforest is governed by indigenous peoples. Indigenous communities see the forest as part of their culture and heritage, respecting and understanding its value and safeguarding it for future generations. Newcomers to the area tend to see the rainforest as something to be exploited in the short-term, particularly for felling valuable old-growth hardwoods and clearing forested areas for cattle ranching.

Panama’s indigenous communities began using UAVs in 2015 with the support of the Rainforest Foundation US and Tushevs Aerials. Tushevs Aerials is a small organisation that designs and builds UAVs and processes data into maps or digital 3D models. It provides training in any aspect of UAV construction, operation, and data use. Since the beginning of this project UAVs have successfully been used to document illegitimate land occupancy and illegal land occupancy and illegal logging by non-indigenous groups.

Armed settlers

The rampant deforestation in the Darien region of Panama perfectly illustrates this dynamic. Islands of rainforest have managed to resist outside pressure from settlers, thanks to the indigenous communities that inhabit and protect them. With the use of a custom-built fixed wing UAV, the Emberá peoples – near the community of Puerto Indio – could spot and survey over 200 hectares of converted forest that has been illegally occupied by cattle ranchers. The communities’ leaders were stunned to witness the extent of the damage. Prior to seeing the aerial imagery, they had thought that there were only about 50 hectares destroyed by illegal ranching.

The occupation and conversion of forested areas occurred several kilometres away from where the indigenous community lives. But because of tensions with the settlers, who are often armed and confrontational, they had not been able to enter the area and document the illegal ranching practices. Using the UAV allowed them to quickly and safely gather data that evidenced the trespass of their territories.

Tino Quintana, the cacique or traditional chief of the 440,000 hectares’ traditional territory, took the lead on presenting the results of the UAV survey to members of several other Emberá communities. These communities are now working together by using aerial imagery documentation to register official complaints with the regional authorities. The government has promised to remove the settlers, and the Emberá communities plan to reforest the area.

Documenting evidence

Governments are often faced with resource shortages, and are frequently unable to respond to all requests for intervention.  Spatially explicit UAV documentation of illegal logging and land occupancy helps government agencies prioritise their efforts, ensuring that a week-long field inspection will collect enough evidence to justify government intervention.

This experience generated further interest in UAV technology among indigenous communities in eastern Panama, inspiring other leaders to ask for UAV support. The Emberá and Wounaan General Congress, which oversees thousands of hectares of rainforest across 27 distinct territories, was given a DJI Phantom 3 Professional quadcopter by the Rainforest Foundation in November 2015. Wounaan leaders flew this UAV within the district of Platanares on the Pacific coast of Panama. The geo-referenced images proved that 10 hectares had recently been burned for cattle grazing in the middle of their territory.


Diogracio Puchicama, a Wounaan indigenous leader, who has been threatened by illegal loggers and settlers for several years, because of his efforts to protect 20,000 hectares of rainforest along the Pacific coast, submitted the UAV-generated documentation to the environmental authorities. Impressed by the accurate geo-referencing of the images documenting forest destruction, the Ministry of Environment promised to be more present in the area and enforce the law.

In late January 2016, Diogracio reported that the authorities had been patrolling the district of Platanares constantly, and that most of the settlers had been at least temporarily removed. ‘I have been denouncing illegal loggers in Platanares for over five years, and the authorities have done nothing, not moved a finger,’ Diogracio Puchicama noted. ‘Now, after they have realised that we have the drone, they are doing their job and enforcing the law. It’s a good sign.’

Protection of indigenous rights

Emberá and Wounaan communities are planning in partnership with the Rainforest Foundation US and the Food and Agriculture Organisation (FAO) of the United Nations to fly UAVs in at least six more indigenous communities in Panama. They will use the imagery to raise awareness among local communities of the ongoing illegal and un-monitored forest destruction within their traditional territories and the need to document and denounce this destruction to the authorities. They will also use the aerial photographs to help Panamanians understand how important forests are, and the essential role that indigenous peoples have played in keeping them intact.

The experience from Panama illustrates that UAVs have the potential to alter the power balance in favour of indigenous communities’ own ability to protect, monitor, and report on their lands, territories, and natural resources. This technology empowers indigenous people to play an active role in safeguarding their lands and to become equal partners – rather than just beneficiaries – to government and civil society agencies, which are involved in conservation and rights’ protection.

Indigenous peoples’ communities, organisations, and their civil society partners in the region and beyond are now very interested in adopting UAVs for conservation or for the protection of indigenous rights and territories. There are further discussions with the Mesoamerican Alliance of Peoples and Forests regarding the use of UAVs in Central America and with an indigenous network in Bolivia. Indigenous communities in Guyana and Indonesia are already using UAVs for land mapping. Also in Africa the Shompole Maasai community in Kenya and a forester in the Democratic Republic of the Congo are interested in using the technology. This shows that the interest in UAVs is growing all around the globe for monitoring illegal land use in indigenous territory.

About the authors:

Nina Kantcheva Tushev (nina.kant@gmail.com) is co-founder of Tushevs Aerials and indigenous peoples’ rights advisor at the UNDP. Tom Bewick (tombewick@rffny.org) is program manager at the Rainforest Foundation US. And Cameron Ellis (jamescameronellis@gmail.com) is principal at Groundtruth Geographics.

Related Links:

Video that demonstrates how Dayaks in Indonesia make use of UAVs.
https://goo.gl/u8Bv2v

Article and video outlining a training in the use of UAVs with indigenous communities in Peru.
https://goo.gl/jhoMFJ

Source: ICT Update # 82

#UAV4Good #landrightsnow #indigenousrights @ICT_Update on #Drones for #Agriculture https://t.co/gwItjPO5tg #UAV pic.twitter.com/wbUhwwlli4

— Drones 4 Agriculture (@UAV4Ag) April 30, 2016