Improving AATSR Geolocation to allow Application in a Multi-Sensor Science Task
Fisher, Daniel; Muller, Jan-Peter

Given the specified 50km2 mission grid resolution of the sea-surface temperature products derived from the Along Track Scanning Radiometer (ATSR) instruments [1], provision for accurate geo-referencing was not of primary concern during the design phase. However, the ATSR instruments have, as expected, been applied to a number of other scientific areas, including: global fire event mapping [2], the stereo photogrammetric determination of cloud top heights [3], and global albedo determination presented in accompanying papers [4,5].

Many of these studies require either validation against other observations, or the integration of multi-sensor datasets. In all instances, accurate geo-referencing is of utmost important to obtain reliable outcomes. Indeed, in the case of the ESA DUE GlobAlbedo, the inclusion of Advanced-ATSR (AATSR) data, due to its poor geo-location accuracy (±2km), was found to significantly degrade the output albedo products accuracy, and hence was excluded from the processing.

Here we demonstrate an approach for improving AATSR geo-location accuracy to a level suitable (<500m) for inclusion into the albedo derivation for the GlobAlbedo prototype sea-ice study [5]. The approach applies an automated tie-point detection and image warping technique previously developed to improve co-registration between the AATSR forward and nadir views to pixel level accuracy [6]. In the case described here, the AATSR nadir imagery is co-registered to MERIS reduced resolution imagery, which is known to have geolocation accuracy to ~160m [7]. Through this relative registration process, absolute geolocation accuracy similar to that of MERIS is achieved for AATSR.

The improvement in the absolute geolocation accuracy of AATSR has been independently assessed against collocated MODIS imagery (~50m geolocation accuracy [8]), and is found, in all instances, to be within the accuracy requirements for inclusion within the GlobAlbedo study.

Reference cited
[1] Vass, P. and M. Handoll, 1991: UK ERS-1 Reference Manual, Royal Aerospace Establishment, Famborough, UK., 131 pp.

[2]Arino, O., & Rosaz, J. M. (1999, June). 1997 and 1998 world ATSR fire atlas using ERS-2 ATSR-2 data. In Proc. Joint Fire Sci. Conf (pp. 177-182). Boise, ID.

[3] Muller, J., M. Denis, R. D. Dundas, K. L. Mitchell, C. Naud, and H. Mannstein (2007), Stereo cloud-top heights and cloud fraction retrieval from ATSR-2, Int. J. Remote Sens., 28, 1921-1938. DOI: 10.1080/0143116060103097

[4] Muller, J.-P., López, G., Watson, G., Shane, N., Kennedy, T., Lewis, P., Fischer, J., Guanter, L., Domenech, C., Preusker, R., North, P.R., Heckel, A., Danne, O., Krämer, U., Zülhke, M., Brockmann, C., Cescatti, A., Pinnock, S. (2013) The ESA GlobAlbedo land surface albedo products from European sensors and their analysis and validation. This Symposium

[5] Muller, J.-P., Fisher, D., Watson, G., Shane, N., Kennedy, T., North, P.R., Heckel, A., Danne, O., Brockmann, C., Stroeve, J., Pinnock, S. (2013) The ESA GlobAlbedo prototype sea-ice albedo products from European & US sensors. This Symposium

[6] Fisher and Muller. Global warping coefficients for improving ATSR co-registration. Remote Sensing Letters (2012) vol. 4 (2) pp. 151-160, DOI: 10.1080/2150704X.2012.713138

[7] accessed 14th February 2013

[8] Wolfe, R. E., Nishihama, M., Fleig, A. J., Kuyper, J. A., Roy, D. P., Storey, J. C., & Patt, F. S. (2002). Achieving sub-pixel geolocation accuracy in support of MODIS land science. Remote Sensing of Environment, 83(1), 31-49.

* work supported under ESA/ESRIN contract 22390/09/I-OL