Airborne Soil Moisture Mapping In Support Of Relief Efforts In Texas During Flooding Events Of 2007
Gasiewski, Albin J 1 ; McIntyre, Eric M 2 ; Manda, Damian 3 ; Klein, Marian 4 ;Wells, Gordon 5 ; Howard , Theresa 6 ; Jackson, Thomas 7
1 CU/ECE Center for Environmental Technology
2 CU/ECE Center for Environmental Technology
3 CU/ECE Center for Environmental Technology
4 Boulder Env. Science & Technology (BEST, LLC)
5 Univ. of Texas at Austin
6 Univ. of Texas at Austin
7 USDA-ARS
The potential for using volumetric soil moisture (SM) data for predicting runoff and flash flood risk depends on both the spatial resolution the data and its timely provision to emergency managers. During a season of exceptionally heavy and sustained convective precipitation in June and early July of 2007 the CU Center for Environmental Technology and NASA assessed the potential capability of airborne soil moisture mapping based on C-band passive microwave radiometry to support flood risk management. The instrument used was the CU Polarimetric Scanning Radiometer (PSR) system operated on the NASA Wallops Flight Facility’s P-3B aircraft (N426NA) and configured with the PSR/CXI C- and X-band scanhead. The PSR provided brightness imagery at a rate of ~11,000 sq km per flight hour with ~3 km spatial resolution and precision of ~1-2K from 7.3 km MSL altitude during two flood risk mapping sorties. The sorties were flown over areas of north and central Texas with suspected near-saturation SM conditions and forecast to receive continued precipitation within the week after each flight.
During the month of June wet weather over Oklahoma and Texas had caused persistent flooding in the region. Persistent thunderstorms during the period from June 18-20 inundated parts of the Red River floodplain around Gainseville, TX and vicinity, causing loss of life and significant flood damage. The extent of this flooding was readily observed as cold signatures in the PSR imagery associated with wet soil and/or standing water.
A flown on July 3, 2007 over an extended region of central Texas prior to forecast precipitation revealed a high degree of wetness soil in the region around San Antonio, N and W-NW of Austin, and around Corpus Christi. The apparent wetness corresponded well with low-lying areas around rivers and lakes, thus suggesting a strong connection to wetness. The SM imagery is compared to FEMA first-floor flood level depths measured W-NW of Austin. A correlation is observed between the location of regions of saturation or standing water and FEMA flood depth. It is believed that these are the first-ever high-resolution microwave maps of soil moisture used to help support flood risk assessment.
To determine how much rainfall is required to cause small-scale flooding, operational weather forecasters currently rely on Flash Flood Guidance (FFG), which is derived from rainfall-runoff models at NOAA/NWS River Forecast Centers (RFC). Currently, soil wetness information foe FFG comes from models and not from observations. Although models continue to improve they cannot always provide a reliable measure of the capacity of soil to absorb rainfall. This study suggest that airborne C- and X-band imaging of SM provides a reliable and potentially valuable means of determining this capacity by remote measurement.