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Sunday, December 17, 2017
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The Benefits of Unmanned Aerial Systems under Cloudy Conditions

At the 9th European Conference on Precision Agriculture, held in Lleida (Spain) the principal benefits of the FieldCopter project were shown and discussed. Benefits of UAS include their flexible deployment at any time in the day and their ability to acquire imagery under cloudy conditions. However, the extent of these benefits had not been previously evaluated, so the project calculated the probability that usable satellite images would be unavailable because of cloud cover.


Satellite services are reasonably mature: the number of earth observation satellites has increased significantly in recent years and their number is expected to increase from 125 in 2012 to 250 by 2017. Despite the increase in satellites, better sensors, better quality images through mosaicing and post-processing, cloud cover poses a major problem for satellite service providers as cloud-free imagery in temperate regions is rare.

Clouds can interfere with satellite imaging in several ways. First of all information cannot be acquired from a cloud-obscured surface, but clouds also affect imaging because of shadows and diverse reflections. Shadows are often ‘displaced’ depending on view angle and cloud height. While cloud masking and other data processing techniques can be used to reduce the effects, they do not obviate the problem for remote sensing support for precision agriculture. Experts stated that a cloud free picture is always preferred, but scenes with up to 20% cloud cover can be acceptable.

Calculations from hourly meteorological data based on images taken from the Dutch National Satellite data portal, showed that satellite-based remote sensing has a 20% probability of producing an adequate image.

Experts in UAS operations identify a number of weather criteria that can restrict UAS operations. The optical remote sensing systems require homogeneous light conditions for optimum performance. For reasons of stability and platform security, the wind speed should be less than 8.0 m/s. Rain affects visibility and also crop response is different for humid crops from those that are dry. When all these criteria are taken into account, this gives a probability of 45% that on any given day a usable image can be acquired. If only the cloud criterion is considered (assuming rain has minimal impact in the summer period), the probability of a usable image rises to 70%.

It was concluded that, regardless of many other benefits of UAS, based on weather conditions alone, UAS can be considered a valuable extension to satellite services and an indispensable platform for service assurance. The complete article can be found under publications.

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FieldCopter is carried out in the context of the Galileo FP7 R&D programme supervised by the GSA (Nr. 277612-2).