Achieving High-Resolution Thermal Imagery in Low-Contrast Lake Surface Waters by Aerial Remote Sensing and Image Registration
A.I. Rahaghi, U. Lemmin, D. Sage, D.A. Barry
Remote Sensing of Environment, vol. 221, pp. 773-783, February 2019.
A two-platform measurement system for realizing airborne thermography of the Lake Surface Water Temperature (LSWT) with ~0.8m pixel resolution (sub-pixel satellite scale) is presented. It consists of a tethered Balloon Launched Imaging and Monitoring Platform (BLIMP) that records LSWT images and an autonomously operating catamaran (called ZiviCat) that measures in situ surface/near surface temperatures within the image area, thus permitting simultaneous ground-truthing of the BLIMP data. The BLIMP was equipped with an uncooled InfraRed (IR) camera. The ZiviCat was designed to measure along predefined trajectories on a lake. Since LSWT spatial variability in each image is expected to be low, a poor estimation of the common spatial and temporal noise of the IR camera (nonuniformity and shutter-based drift, respectively) leads to errors in the thermal maps obtained. Nonuniformity was corrected by applying a pixelwise two-point linear correction method based on laboratory experiments. A Probability Density Function (PDF) matching in regions of overlap between sequential images was used for the drift correction. A feature matching-based algorithm, combining blob and region detectors, was implemented to create composite thermal images, and a mean value of the overlapped images at each location was considered as a representative value of that pixel in the final map. The results indicate that a high overlapping field of view (~95%) is essential for image fusion and noise reduction over such low-contrast scenes. The in situ temperatures measured by the ZiviCat were then used for the radiometric calibration. This resulted in the generation of LSWT maps at sub-pixel satellite scale resolution that revealed spatial LSWT variability, organized in narrow streaks hundreds of meters long and coherent patches of different size, with unprecedented detail.
@ARTICLE(http://bigwww.epfl.ch/publications/rahaghi1901.html, AUTHOR="Rahaghi, A.I. and Lemmin, U. and Sage, D. and Barry, D.A.", TITLE="Achieving High-Resolution Thermal Imagery in Low-Contrast Lake Surface Waters by Aerial Remote Sensing and Image Registration", JOURNAL="Remote Sensing of Environment", YEAR="2019", volume="221", number="", pages="773--783", month="January", note="")