Sensor Demonstrates Hydrological Mapping Capabilities During SMEX04/NAME

September 21, 2005

Airborne remotely-sensed measurements of soil moisture provide a valuable new means of quantifying the surface moisture state. When such measurements are made diurnally over a wide area they can also be used to quantify surface latent heat flux. In addition, surface soil moisture maps can be used to understand runoff and storage mechanisms and assess runoff potential during precipitation events, thus contributing an important flash flood warning capability. Trends in soil moisture also reflect climate and regional weather, and affect drought and fire danger levels.

During the 2004 Soil Moisture Experiment/North American Monsoon Experiment (SMEX04/NAME) the NOAA Environmental Technology Laboratory fielded their Polarimetric Scanning Radiometer (PSR) as the principal research instrument on a Navy P-3 research aircraft. The PSR provided wide-area mapping of soil moisture at two 50 x 75 km sites: one in southern Arizona at the Walnut Gulch watershed and one in northern Mexico in the Sonora region.

As presented at the 2005 International Geoscience and Remote Symposium in Seoul, Korea, a recent analysis of the ETL PSR data has illustrated with unprecedented detail the importance of soil type in hydrological uptake and runoff. Forecasting of mesoscale convection requires detailed knowledge of the thermodynamic state of the atmosphere, including moisture, temperature, clouds, and winds. It also requires knowledge of sources of moisture that force the atmosphere. To this end, evaporation of surface water has a considerable impact on convective activity by increasing the amount of moisture immediately in and above the boundary layer, increasing the flux of latent heat into the atmosphere, and decreasing the stability of the boundary layer. Mesoscale forecasting models need to account locally for such surface moisture fluxes, which are a function of insolation, topography, vegetation coverage and type, and soil type and dryness.

When compared with radar-based precipitation data the PSR data from SMEX04/NAME clearly showed the rapid evaporation and runoff mechanisms characteristics of rocky soil covered by sparse vegetation typical of a desert environment. While previous soil moisture maps obtained over loamy soil in Iowa and Oklahoma reproduced the footprints of precipitation cells, the SMEX04/NAME data showed most of the measured precipitation running off through arroyos toward dry lake beds located within the watershed. The unusually large amounts of runoff versus uptake provide compelling evidence of the need for coupling comprehensive surface hydrological models with atmospheric forecast models.

The SMEX04/NAME campaign built on preceding experiments (SGP99, SMEX02 and SMEX03) by focusing specifically on topography, vegetation and strengthening the soil moisture components of NAME. One of the main objectives of NAME was to improve prediction of warm season precipitation which is highly dependent on convection, which, in turn, is controlled, at least in part, by soil moisture and surface temperature. Therefore, an accurate characterization of spatial and temporal variability of soil moisture was important to NAME for i) initialization and updating of boundary conditions for the land surface component of land-atmosphere models, ii) validation of land surface model outputs, and iii) discerning the relationships between soil moisture and warm season precipitation and associated feedback mechanisms. In addition to the several C- and X-band polarimetric channels on the PSR the previous build of the instrument (PSR/CX) was modified to include a broadband frequency-swept spectrometer for interference mitigation studies (PSR/CXI) in support of the Nation?s NPOESS program.

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Albin Gasiewski