Vol. 13, Special Issue 1: 34th EARSeL Symposium, 53-58, 2014

RGBI images with UAV and off-the-shelf compact cameras: an investigation of linear sensor characteristics
Ralf Gehrke, and Ansgar Greiwe

UAVs are able to close the gap between ground-based (total station, Global Navigation Satellite System - GNSS) and airborne data acquisition. Usually, cameras in the visible range of light are used for this purpose. Until now, only a few sensors have been commercially available for the capturing of non-visible wavelengths, e.g., of the near infrared for vegetation analysis. Almost all common camera sensors can be used and be modified through small interventions for the near infrared to make a RGBI (red, green, blue, near infrared) sensor head. Vegetation parameters like NDVI can be calculated from this data.

At the Frankfurt University of Applied Sciences, a sensor head has been developed to collect RGBI data. The sensor head consists of two Sigma DP2 FOVEON-sensor cameras. One of them is modified for the near infrared. This sensor head is mounted to an octocopter UAV with a maximum take-off weight of 3.5 kg. The cameras are triggered simultaneously. In the post-processing, the image channels are registered to each other by a self-developed software script and a radiometric adjustment based on reference targets in the field is carried out. The resulting multispectral images are processed to multispectral orthophoto mosaics in standard photogrammetric software. A spectrometer and various test panels are available for the investigation of linear characteristics of the cameras.

This paper briefly presents the construction of the sensor head. In particular, the radiometric characteristics of the sensor should be considered. The Sigma cameras have a poor colour separation due to the installed FOVEON sensors. This is balanced by the algorithms implemented in the raw data software Sigma PhotoPro, offered by the manufacturer. However, the linear sensor characteristic is destroyed by gamma correction and white balance. Freely available raw data converters can process the Sigma data without these photographic corrections and preserve the linear characteristic, but the image quality suffers from the poor spectral separation.

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DOI: 10.12760/02-2014-1-10

Submitted: 31 Mar 2014
Revised: 4 Aug 2014
Accepted: 14 Aug 2014
Published: 8 Sept 2014
Responsible editor: Rainer Reuter

Gehrke R & A Greiwe, 2014. RGBI images with UAV and off-the-shelf compact cameras: an investigation of linear sensor characteristics. EARSeL eProceedings, 13(S1): 53-58

EARSeL European Association of Remote Sensing Laboratories, Strasbourg, France


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