tanbul 2004 
ce for their 
Observing 
nsors, and 
nsors and 
9. 
ompression 
nane, May 
dex, e.html 
' sensor for 
SPIE, vol. 
Observing 
Promotion 
LOS", pp. 
lona, Sept. 
USE OF SATELLITE REMOTE SENSING IN 
HYDROLOGICAL PREDICTIONS IN UNGAGED BASINS 
Venkat Lakshmi, PhD, P.E. 
Department of Geological Sciences, 
University of South Carolina, Columbia SC 29208 
(803)-777-3552; (803)-777-6684 (Fax); venkat-lakshmi@sc.edu 
TS SS 11 
KEY WORDS: Hydrology, Microwave Remote Sensing, Ungaged Basins 
Abstract 
Ungaged basins pose a challenge to hydrological studies as they lack both calibration and validation data for the use of 
land surface models. Therefore, one has to use the satellite data that is available which describes the aspects/attributes 
of the basin from a hydrological perspective. Soil moisture is routinely mapped by the Advanced Microwave Scanning 
Radiometer (AMSR). Vegetation is characterized by MODIS (Moderate Resolution Imaging Spectroradiometer) and 
surface temperature is estimated using AIRS (Advanced Infra-Red Sounder) as well as MODIS. Precipitation is 
measured (in the tropical regions) from the TRMM (Tropical Rainfall Measuring Mission) Microwave Imager (TMI) 
with the Global Precipitation Mission (GPM) due to be launched in a few years. The synergistic use of these data sets 
along with hydrological models would help us to (a) input precipitation and vegetation information into a hydrological 
model and calculate the soil moisture and surface temperature using the water and energy balance equations (b) the 
measured soil moisture and surface temperature can be used in two ways (i) to calibrate certain model parameters (ii) to 
verify the output of the model through validation. The overland runoff from the hydrological model would be routed in 
the stream channel network (obtained from the Digital Elevation Data) to obtain the streamflow at the catchment outlet. 
This would help in estimation of the water resources for the watershed. This paper will describe the state of the art 
knowledge in combining remote sensing, hydrological modeling and data assimilation. 
1.0 Introduction 
Land surface hydrology is an accounting of the 
water received (precipitation) and water lost 
(evaporation, runoff from land, streams to oceans) and 
the gain in water storage (rise in level of inland water 
bodies, increase in soil moisture, snow and, rise in water 
table). This accounting is based on a simple water 
balance principle, i.e. a conservation of mass. However, 
as evapo-transpiration (loss of water due to evaporation 
from the land surface and loss of water from the plant 
stomata due to transpiration) involves energy, the 
hydrological budget involves a coupled water and energy 
balance. 
However, quantification of the hydrological 
budget is extremely difficult over large spatial domains 
and over large time periods through direct observations 
as in-situ observations are labor intensive as well as 
expensive. This is specifically the case in un-gauged 
basins wherein stream flow data are absent or 
insufficient and little or no observations of spatially 
variable hydrological quantities are carried out. This 
makes it extremely difficult to carry out hydrological 
modeling for predictions of water resources. Satellite 
remote sensing provides a methodology to overcome 
these issues with a broad spatial coverage and a repeat 
temporal coverage. 
Of the hydrological variables derived using 
satellite data, precipitation (both by radar and satellites) 
313 
is perhaps the one most extensively studied. Precipitation 
patterns are highly variable in space and time. Exclusive 
dependence on remotely sensed precipitation would not 
result in an adequate characterization of the state of the 
watershed in order to estimate stream flow as land areas 
exhibit heterogeneities in soils, topography, roughness 
and vegetation. Therefore, a simple translation of rainfall 
into runoff is not possible so there is a need to utilize the 
readily available satellite images of other hydrological 
variables such as — soil moisture, surface temperature, 
vegetation, air temperature along with those of 
precipitation. 
In this paper, we describe the various satellite 
data sets that can be used to generate land surface 
hydrological variables followed future challenges and 
limitation to the use of satellite remote sensing in the 
context of PUB. 
2.0 Satellite Data sets and their role in land 
surface hydrology. 
This section of the paper describes the different data 
sets that are used in land surface hydrological research. 
References provide more complete documentation on 
satellite data products, their accuracy, spatial and 
temporal resolution and applicability. In hydrology, soil 
moisture, precipitation, runoff, evaporation (through air 
temperature and surface humidity), transpiration (similar 
to evaporation, plus added vegetation content), surface 
temperature, incoming short and long wave radiation