Bob L. Weber

High-Resolution Airborne Polarimetric Microwave Imaging of Snow Cover During the NASA Cold Land Processes Experiment

We present a detailed analysis of the airborne passive microwave remote-sensing data that were collected at a broad range of microwave bands and at a high spatial resolution during the 2002 and 2003 National Aeronautics and Space Administration Cold Land Processes Experiment (CLPX). An accurate measurement of snowpack properties using passive microwave observations requires the detailed knowledge of the relationship between snowpack geophysical parameters and the upwelling polarimetric brightness signature. The principle microwave instrument used for the CLPX was the polarimetric scanning radiometer (PSR), which provided ~100-m resolution maps of the snow emissivity at all Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) bands during several intensive observation periods over the Colorado Rocky Mountains. The observed conditions included drought, normal snowpack, and spring snowmelt. The PSR and related ground-based observations of snowpack properties made during the 2002 and 2003 CLPX campaigns provide a comprehensive high-resolution passive microwave data set. Results show that the high-resolution PSR data exhibit emissivity modes that are similar to those observed in the historical data sets, and that the empirical relationships between the emissivity and the snow water equivalent (SWE), after the effects of macrovegetation are removed, closely match those found in the past theoretical studies. The use of the 89-GHz channel in the empirical relationships provides improved accuracy under dry snow conditions and a small SWE; however, the variability of the SWE-emissivity relationships increases with an increasing SWE. A summary of the observed relationships between the emissivity spectra of snow and snowpack properties is presented. Comparison of the total water content from the AMSR-E and PSR observations shows that the satellite measurements underestimated the total volume of water storage from airborne observations on the average by a factor of five.

Initial results from the 2004 North Slope of Alaska Arctic winter radiometric experiment

A multiinstrument radiometric experiment was conducted on the North Slope of Alaska near Barrow, Alaska, during March 9 to April 9 2004. Initial radiometric and radiosonde data from this experiment are presented.

Geosynchronous microwave (GEM) sounder/imager observation system simulation

Precipitation sensitivity calculations suggest that a geosynchronous microwave (GEM) sounder/imager using millimeter- and submillimeter-wave channels at 50-57, 118, 183, 340, 380, and 424 GHz with a 2-3 meter diameter real aperture antenna will provide time-resolved radiance data valuable for tracking convective precipitation events using a numerical weather prediction (NWP) model. Presented are scattering-based Jacobian simulations of a landfalling hurricane that illustrate the capabilities of GEM for precipitation measurement and NWP-based radiance assimilation.

Soil moisture experiments 2004 (SMEX04) polarimetric scanning radiometer, AMSR-E and heterogeneous landscapes

An unresolved issue in global soil moisture retrieval using passive microwave sensors is the spatial integration of heterogeneous landscape features to the nominal 50 km footprint observed by most satellite systems. One of the objectives of the Soil Moisture Experiments 2004 (SMEX04) was to address some aspects of this problem, specifically variability introduced by topography and convective precipitation. Other goals included understanding the role of the land surface in the North American Monsoon System. Data were collected during the month of August 2004 at three scales; ground based point measurements, aircraft passive microwave mapping, and satellite observations using AMSR-E and other sensors. SMEX04 was conducted over two regions: Arizona - semi-arid climate with sparse vegetation and moderate topography, and Sonora (Mexico) - moderate vegetation with strong topographic gradients. The Polarimetric Scanning Radiometer (PSR/CX) was flown on a Naval Research Lab P- 3B aircraft as part of SMEX04 (11 dates of coverage over Arizona and 10 over Sonora). General meteorological conditions, the PSR/CX data sets and selected comparisons of this data to AMSR-E are presented. Field experiments in support of remote sensing, hydrology and climate have included catchments throughout North America. These experiments have been intensive efforts ranging from one to six weeks in duration. The basic approach used in these experiments has been to collect ground-based samples of soil moisture in conjunction with aircraft flights at the same time as satellite overpasses. The aircraft instruments operate in low frequency microwave wavebands that are well suited for the measurement of soil moisture. The aims of these experiments have been: validation of remotely sensed data from aircraft and/or space-borne microwave sensors, the mapping of spatial and temporal variability of soil moisture, the relationship of soil moisture to vegetation and the near-surface atmospheric characteristics, and the collection of in-situ gravimetric data for soil moisture for validation of the land surface hydrological models used to simulate the watershed at pre- specified spatial and temporal resolutions. SMEX04 builds on preceding experiments by focusing specifically on topography, vegetation and strengthening the soil moisture components of the North American Monsoon Experiment (NAME) (http://www.joss.ucar.edu/name). One of the main objectives of NAME is to improve prediction of warm season precipitation. Warm season precipitation 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 is critical to NAME. This paper focuses on preliminary results from the SMEX04 aircraft campaign involving the PSR/CX and relationships between the aircraft and satellite observations. Additional details on SMEX04 can be found at http://hydrolab.arsusda.gov/smex04.

Median Filter Effects on Radar Wind Profiler Spectral Noise Statistics

AbstractRadar wind profiler (RWP) systems observe radar returns from refractive index fluctuations due to clear-air turbulence. The Doppler spectra used to compute the moments of the returned signal always include noise from various sources and may contain multiple signals. A critical first step in detecting signals is the objective determination of the noise level in each spectrum. Several spectra may be averaged to improve signal detection. In addition to or instead of a mean, a median may be applied to successive spectra in order to reject transient interference. Monte Carlo simulations were used to examine the effects of the median versus the mean on the objective noise determination. When a median is used, it was found the noise statistics calculations must be slightly modified.

An interference mitigation technique for passive remote sensing of soil moisture

Anthropgenic interference from terrestrial sources of microwave emission have been observed in passive Cband radiometric data using both the NOAA Environmental Technology Laboratory’s (ETL) PSR/CX airborne imaging instrument, and the JAXA AMSR-E instrument on the NASA EOS Aqua satellite. Simultaneous observations using multiple ~300 MHz subbands, incorporated into the PSR/CX instrument, have provided one means of interference mitigation that is useful under moderately contaminated conditions. ETL has developed a new C-band spectrometer that observes emissions within relatively narrower bandwidths and is tunable from 5.8 to 7.5 GHz. The spectrometer is able to reduce the effects of the interference at the expense of radiance sensitivity and observation time. Preliminary data analysis suggests the spectrometer to be an effective component for improving the accuracy of remotely sensed soil moisture measurements using C-band radiometry.

Airborne measurement of snow cover properties using the polarimetric scanning radiometer during the Cold Land Process Experiments (CLPX02-03)

Multispectral polarimetric microwave brightness temperature maps of snowpack in the Colorado Rocky Mountains were obtained using the NOAA Polarimetric Scanning Radiometer (PSR) during three Cold Land Processes Experiments (CLPX) in February 2002, February 2003, and March 2003. The PSR CLPX data offers unique high-resolution information about snow extent, polarimetric emissivity, and snow water equivalent at scales commensurate with natural inhomogeneities in terrain and precipitation patterns. The data is being used for several purposes including snowpack and snowmelt hydrology, calibration and validation of the AMSR-E sensor, cryospheric satellite sensor design, wideband snow emissivity modeling, and snowpack change detection. Initial results from CLPX02 using the PSR/A scanhead are presented showing brightness temperature, emissivity, and estimated snow water equivalent (SWE) maps.

The DeTect Inc. RAPTOR VAD-BL Radar Wind Profiler

AbstractThe DeTect Inc. RAPTOR velocity–azimuth display boundary layer (VAD-BL) radar wind profiler is a pulsed Doppler radar used to make automatic unattended measurements of wind profiles in the lower atmosphere. All data products are produced on site, in real time, and utilize quality control software to screen out interference. The nominal frequencies are 915 and 1290 MHz but other frequencies can be accommodated. While the architecture is similar to other boundary layer wind profilers, the RAPTOR VAD-BL is designed to provide consistently superior data quality due to its antenna design and signal processing capabilities. The antenna is a high-performance parabolic reflector with a feed that is designed in house for the operational frequency of the radar. The antenna is mounted on a robust military-grade azimuth-only positioner. The RAPTOR VAD-BL can collect data from several opposing beam positions with the goal of producing higher-quality wind data using the velocity–azimuth display (VAD) algorithm....

Parametrization of an anisotropic ocean surface emissivity model based on WindSat polarimetric brightness observations

The goal of this research has been to develop a standardized fast full-Stokes ocean surface emissivity model with Jacobian for a wind-driven ocean surface applicable at arbitrary microwave frequencies, polarizations, and incidence angles. The model is based on the Ohio State University (OSU) two-scale code for surface emission developed by Johnson (2006, IEEE TGRS, 44, 560) as presented in our 2012 URSI talk. A total of five physical tuning parameters for the model were identified, including the spectral strength and the hydrodynamic modulation factor. The short wave part of the sea surface spectrum is also allowed to have an arbitrary ratio relative to the long wave part. The foam fraction is multiplied by a variable correction factor, and also modulated to allow an anisotropic foam fraction with more foam on the leeward side of a wave.

An anisotropic ocean surface emissivity model based on WindSat polarimetric brightness observations

A full-Stokes vector model for the microwave emissivity of an anisotropic wind driven ocean surface based on measured satellite data and using a two-scale model for surface emission is being developed for the purpose of assimilation of satellite microwave radiances. The model is based on the Ohio State University two-scale model and tuned to WindSat full-Stokes emissivity data as analyzed by Meissner and Wentz. Several physical inconsistencies were corrected in the model. The tuned model results over a range of wind speeds from 0-20 m/sec show good agreement in the 0th, 1st, and 2nd azimuthal brightness temperature harmonics. A bias model for the tuned model was developed to account for residual discrepancies.