Abstract
Field-based soil moisture measurements are cumbersome. Remote sensing techniques based on active or passive microwave data have limitations. This paper presents and validates a new method based on land surface energy balances using remotely sensed optical data (including thermal infrared), which allows field and landscape-scale mapping of soil moisture depth-averaged through the root zone of existing vegetation. Root zone depth can be variable when crops are emerging. The pixel-wise "evaporative fraction" (ratio of latent heat flux to net available energy) is related to volumetric soil moisture through a standard regression curve that is independent of soil and vegetation type. Validation with measured root zone soil moisture in cropped soils in Mexico and Pakistan has a root mean square error of 0.05 cm3 cm-3: the error is less than 0.07 cm3 cm-3 in 90% of cases. Consequently, soil moisture data should be presented in class intervals of 0.05 cm3 cm-3. The utility of this method is demonstrated at the field scale using multitemporal thematic mapper imagery for irrigated areas near Cortazar in Mexico, and for river basin-scale water resources distribution in Pakistan. The potential limitation is the presence of clouds and the time lag between consecutive images with field-scale resolution. With the falling price of optical satellite imagery, this technique should gain wider acceptance with river basin planners, watershed managers, and irrigation and drainage engineers.
Original language | English (US) |
---|---|
Pages (from-to) | 326-335 |
Number of pages | 10 |
Journal | Journal of Irrigation and Drainage Engineering |
Volume | 129 |
Issue number | 5 |
DOIs | |
State | Published - 2003 |
Keywords
- Imaging techniques
- Irrigation
- Mapping
- Remote sensing
- Soil water
- Water resources
- Watersheds
ASJC Scopus subject areas
- Civil and Structural Engineering
- Water Science and Technology
- Agricultural and Biological Sciences (miscellaneous)