.c.Chickasha, Oklahoma 


Titles of Investigations:

I.  Applications of SIR-C/X-SAR Synthetic Aperture Radar
to Hydrology

II.  SIR-C/X-SAR Measurements of Soil Moisture, Vegetation
and Surface Roughness, and Their Hydrological Application

Principal Investigators:

I.  Ted Engman
  Goddard Space Flight Center

II.  James Wang
  Goddard Space Flight Center

Site Description:

 The Little Washita River Watershed covers 235.6 square miles
and is a tributary of the Washita River in southwest Oklahoma
 (Fig. 1).  The watershed is in the southern part of the
Great Plains of the United States.  The climate is classified
as moist and subhumid; the average annual rainfall was 29.42
inches for the 24 years of data collection by the Agricultural
Research Service.  Summers are typically long, hot, and relatively
dry, and winters are typically short, temperate, and dry
but are usually very cold for a few weeks.  Much of the annual
precipitation and most of the large floods occur in the spring
and fall.  A more detailed review of the climate and its
variability for this watershed and the surrounding area is
presented by the Staff, Water Quality and Watershed Research
Laboratory (1983) (Allen, P. B. and Naney, J. W., 1991).
 The Little Washita River Watershed in southwest Oklahoma
is unique in that over a period of several years it has had
an unusually large amount of soil and water conservation
treatment and research.  In 1936 the eastern portion of the
watershed was chosen as part of a national demonstration
project for soil erosion control.  In the late 1930s the
Civilian Conservation Corps did extensive erosion control
work, including terracing, drop-structure building, gully
plugging, and tree planting.  Since establishing county offices
in the 1940's, the U. S. Department of Agriculture's (USDA)
Soil Conservation Service (SCS) has applied extensive soil
and water conservation structures and measures, including
terraces, diversions, farm ponds, floodwater-retarding reservoirs,
gully plugging and smoothing, scrub timber removal, and land
use planning.
 In 1961, the USDA's Agricultural Research Service, in compliance
with U. S. Senate Document 59 (1959), began collecting hydrologic
data on the Little Washita River Watershed and other watersheds
in the vicinity to determine the downstream hydrologic impacts
of the SCS floodwater-retarding reservoirs.  This data collection
process involved an intensive rain gauge network and a stream
gauging station near the watershed outlet that provided data
on continuous flow, suspended sediment transport, and, for
a few years, water quality.  Data on groundwater levels and
channel geometry were also collected to determine possible
effects of the treatment program.
 In 1978, this watershed was one of seven watersheds chosen
across the nation for the Model Implementation Project (MIP),
which was jointly sponsored and administrated by the USDA
and the U. S. Environmental Protection Agency.  The main
objective of the MIP was to demonstrate the effects of intensive
land conservation treatments on water quality in watersheds
that are larger than about 25 square miles.

 Objectives:

I.  a) Determine and compare soil moisture patterns within
one or more humid watersheds using SAR data, ground-based
measurements, and hydrologic modeling.

  b) Characterize the hydrologic regime within a catchment
and identify the runoff producing characteristics of humid
zone watersheds.

  c) Use radar data as the basis for scaling up from small
scale, near-point process models to larger scale water balance
models necessary to define and quantify the land phase of
GCMs.

II.  a) Analyze the SIR-C/X-SAR response to soil moisture,
vegetation, and surface roughness.

  b) Combine the visible and near-infrared data with the
SIR-C/X-SAR data to improve the range and accuracy of vegetation
classification.

  c) Test theoretical models for microwave propagation with
SIR-C/X-SAR and microwave radiometric measurements over rough
surfaces.

  d) Evaluate a water balance model using SIR-C/X-SAR derived
soil moisture values and other ancillary data.

Field Measurements:

I. a) WASHITA-92 is a Multisensor Airborne Campaign (MAC)
for hydrology (MACHYDRO) that was conducted at the Chickasha
supersite during the period of June 8-18, 1992.  This experiment
emphasized the microwave sensors on the two NASA aircraft;
the C-130 and the DC-8.  Listed below are the instruments
flown by the two aircraft.

  C-130 Thermal Infrared Multispectral Scanner (TIMS)
    Thematic Mapper Simulator (NS001)
    Electronically Scanning Thinned Array Radiometer (ESTAR)
    Cameras
    37 GHz radiometer
    Laser Profiler (from the USDA)

  DC-8 Synthetic Aperture Radar (SAR) - C-, L-, and P- bands,
polarimetric

 b) During WASHITA-92 a large number of field measurements
were made to support and to provide detailed hydrologic data
for analysis.  Approximately sixty people, scientists, students,
and technicians took part in these ground data collection
activities.  The field data collected included both the routine
hydrology data (rainfall, runoff, met data) and special data
for the experiment, including:

    Micrometer measurements (eddy correlation, Bowen ratio,
etc.)
    Boundary layer profiling (radiosondes)
    Land cover and vegetation mapping
    Surface roughness
    Profile soil and surface soil moisture (grid and transects)
    Bulk density measurements
    Reflectance and emissivity
    Truck based L-band radar and trihedral corner reflectors
    Salinity and lake water temperature
    Satellite data (SPOT, ERS-1, AVHRR)
 c) The meterological conditions during the experiment enabled
us to follow a long but gradual dry-down of the soil moisture.
 Previous to the first flights (June 10), there had been
26 consecutive days of rain in Oklahoma and conditions were
extremely wet with a considerable amount of standing water.
 The last rain over the watershed occurred on the morning
of June 9 and good drying conditions prevailed until after
the last flight on June 18.

 d) The WASHITA-92 experiment will provide a good background
to the up-coming SIR-C/X-SAR missions.  During the mission,
many of the same measurements will be made but the emphasis
will be on a few detailed measurements at selected sites.
 These will be used to verify the radar performance and to
provide the bridge between the WASHITA-92 and the SIR-C/X-SAR
experiments.

II.  Activities of the ground truth data collection, as well
as other relevant satellite and ancillary data acquisitions.

Crew Observations:

1)  Crew Journal: Describe the weather, cloud cover, and
the vegetation at the site.

2)  Cameras: Hercules and Hasselblad will be used to photograph
the site.  Low sun angle images are requested.

Coverage Requirements:

 The minimum coverage requirements for this site are three
(3) passes.

Anticipated Results:

I.  a) Development of a technology for measuring soil moisture
in natural catchments for humid regions using spaceborne
radar.

  b) Development of a new way to characterize the contributing
areas of natural, humid zone catchments.

  c) Development of a technology for modeling soil moisture
distributions in natural catchments based on spaceborne measured
data.

  d) Development of procedures for parameterizing macro-scale
models capable of representing the land phase processes for
GCMs.

  e) Development of procedures to scale up hydrologic processes
from point or small area to catchment scales using SAR data.

  f) Validation of vegetation models for estimating the backscatter
component of overlying vegetation canopies and the underlying
soil condition.

II.  a) Development of an algorithm to retrieve the SIR-C/X-SAR
soil moisture, vegetation and surface roughness parameters.

  b) The relationship between surface parameters and imaging
radar signatures will be established.  An algorithm based
on this relationship to retrieve the surface parameters will
be developed. 

  c) Verify that an imaging radar system with multiple frequencies
and polarizations is an efficient tool for vegetation classification.
 Assessment will be made of the classification scheme improvement
when visible and near-infrared data are included. 

  d) Using SIR-C/X-SAR and ground measured roughness data,
assess the validity of current theoretical models for microwave
backscatter from rough surfaces.

  e) Using the SIR-C/X-SAR retrieved soil moisture and other
ancillary data, verify the validity and limitation of a generalized
water balance model.