Quantitative Evaluation of Landsat 7 ETM+ SLC-off Images for Surface Velocity Estimation of Mountain Glaciers
Abstract:In many cases the Landsat mission series (Landsat 1-5, 7 and 8) provide our only detailed and consistent data source for mapping the global glacier changes over the last 40 years. However, the scan-line corrector (SLC) of the ETM+ sensor on board Landsat 7 permanently failed, resulting in wedge-shaped data gaps in SLC-off images that caused roughly 22% of the pixels to be missed. The SLC failure has left a serious problem for the glacial applications of ETM+ data, particularly for monitoring long-term glacier dynamics in High Asian Mountain where has few available data due to the frequently cloudy covers.
This study aims to evaluate the potential of the Landsat 7 SLC-off images in deriving surface velocities of mountain glaciers. A pair of SLC-off images over the Siachen glacier acquired in Aug 2009 and 2010 was used for this purpose. Firstly, two typical filling-gap methods, the localized linear histogram match (LLHM) and the weighted liner regression (WLR), were utilized to recover the mentioned SLC-off images. Subsequently these recovered pairs were applied for deriving glacier-surface velocities with the COSI-Corr feature tracking procedure. Finally, the glacier velocity results were quantitatively compared with that of a pair of Landsat-5 TM images acquired nearly at the same time with the SLC-off pair.
Our results show that (1) the WLR method achieves a better performance of gap recovering than the LLHM method, (2) the surface velocities estimated with the recovered SLC-off images are highly agreement with those of the TM images, and (3) the annual mean velocity of the Siachen glacier is approximately 70 m/yr between 2009 and 2010 with a maximum of 280 m/yr close to the glacial equilibrium line that are similar with the results in previous studies. Therefore, if a suitable filling-gap method is adopted, e.g. the WLR method, it is highly feasible that the ETM+ SLC-off data can be utilized to estimate the surface velocities of mountain glaciers.