Satellite Imagery Evaluation of Soil Moisture Variability in the Ganges Basin, India
Abstract
Soil moisture (SM) variability across the Ganges Basin in India from the Tista River on the east to the Ghanghra River on the west was assessed using Landsat TM Band 6 imagery dating from 1999-2003. The region contains many large fans (megafans) that have different degrees of incision. The Band 6 thermal channel of Landsat is sensitive to soil temperature variability resulting from differences in moisture content and as such is a proxy for soil moisture variability in this environment. In order to take advantage of this relationship we analyzed the imagery in two steps. First, a Maximum Likelihood Classifier (ML) was used to segment the fans into seven classes. On the Tista fan, thermal characteristics suggest that soils from the proximal and distal portions of the fan are in different thermal/moisture classes indicating a change in the thermal signal from the apex to the toe of the fan. In an attempt to quantify these differences we performed a second level of analysis focusing on the range of thermal values across the fans. This range calculation separates the dry and wet soils on the basis of variability in their moisture content throughout the year. Soils that have a high range (high variability) probably dry up significantly after the monsoon, while those that exhibit a low range indicate either constant wet or dry conditions and/or vegetation that does not vary seasonally. Ground based assessments of soil characteristics on the Tista and Kosi fans supports this image analysis and leads to the following conclusions, 1) Tista megafan, a fan known to be incised and older than the other fans of this basin, shows a distinct change in soil moisture from apex to its toe. This variation is reflected in the increasing presence of wetlands (shallow water table) and the fining of grain size down-the-megafan; 2. Similar temporal variation in SM values is not apparent in Kosi and Gandak megafans where SM shows uniformly low variation from apex to toe. We ascribe this to the younger age and aggrading nature of the megafans; 4. Ghangra megafan, occurring about 400 km west of the Tista megafan, in contrast to other megafans shows a high variability of SM uniformly throughout it. This probably reflects presence of drier soils all through the megafan in response to drier climate to the western part of the alluvial plain.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMEP21B0705B
- Keywords:
-
- 0540 COMPUTATIONAL GEOPHYSICS / Image processing;
- 1866 HYDROLOGY / Soil moisture