[Show abstract][Hide abstract] ABSTRACT: Accurate measurements of water vapor in the Arctic winter, either in situ or remote, are difficult to achieve. These measurements are important to studies in infrared radiative transfer. To focus on measurements during cold temperatures (<- 20ºC) and low amounts of vapor (Precipitable Water Vapor, 5 mm), an Intensive Operating Period (IOP) was conducted at the U.S. Department of Energy’s
[Show abstract][Hide abstract] ABSTRACT: In a recent paper by Mattioli et al., a significant difference was observed between upper-tropospheric and lower-stratospheric water vapor profiles as observed by two radiosonde systems operating in the Arctic. The first was the Vaisala RS90 system as operated by the U.S. Department of Energy's Atmospheric Radiation Measurement Program; the second was the operational radiosondes launched by the U.S. National Weather Service that used the Sippican VIZ-B2 type. Observations of precipitable water vapor by ground-based microwave radiometers and GPS did not reveal these differences. However, both the microwave radiometer profiler (MWRP) and the ground-based scanning radiometer (GSR) contain channels that receive a sig- nificant response from the upper-tropospheric region. In this paper, it is shown that brightness temperature (Tb) observations from these instruments are in consistent agreement with calculations based on the RS90 data but differ by several degrees with calculations based on the VIZ radiosondes. It is also shown that calculations of Tb can serve as a gross quality control of upper-tropospheric soundings.
Journal of Atmospheric and Oceanic Technology 10/2008; 25(10). DOI:10.1175/2008JTECHA1078.1 · 1.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Measurement of water vapor and cloud liquid during very cold (-20 to -40 Deg. C) and dry (precipitable water vapor < 5 mm) conditions is a very important, but difficult task. Starting in 1999, three radiometric experiments were conducted at the U. S. Department of Energypsilas Atmospheric Radiation Measurement (ARM) Programpsilas North Slope of Alaska (NSA) field site near Barrow, Alaska. Principal results from the first two experiments are summarized. Most recently, the Radiative Heating in Underexplored Bands Campaign (RHUBC) was conducted in February-March 2007. The millimeter- and submillimeter-wave channels of the ground-based scanning radiometer (GSR) are very sensitive to low water vapor and cloud contents and allow for accurate observations in the extremely dry and cold conditions typical of the Arctic. Moreover, window channels (e.g., at 90 and 340 GHz, both with horizontal and vertical polarizations) show a high sensitivity to Artic clouds over an extended range of liquid water path (LWP). For RHUBC, during conditions when the precipitable water vapor (PWV) was less than 2 mm, these radiometers were supplemented by frequent Vaisala RS92 radiosonde observations at the ARM site. In this paper, representative PWV and LWP retrievals from the GSR and several ARM instruments are compared. Based on comparisons with 87 RS92 RAOB launches, GSR PWV retrievals achieved almost unprecedented accuracy of 0.1 mm, or about 6 % of the mean PWV during the operating period.
Microwave Radiometry and Remote Sensing of the Environment, 2008. MICRORAD 2008; 04/2008
[Show abstract][Hide abstract] ABSTRACT: A One Dimentional Variational (1DVAR) retrieval technique has been developed for obtaining temperature and humidity profiles from observations of the Ground-based Scanning Radiometer (GSR) operating at millimeter and submillimeter waves. The GSR participated in two Arctic experiments held at the Atmospheric Radiation Measurement (ARM) Program in Barrow, Alaska: the Water Vapor Intensive Operational Period (WVIOP, March-April 2004) and the Radiative Heating in Underexplored Bands Campaign (RHUBC, February-March 2007); data from both experiments are used in this paper. Temperature and humidity profiles retrieved with the 1DVAR technique are compared with simultaneous radiosonde observations. Examples and statistical results are presented and discussed to demonstrate the achieved retrieval accuracy and vertical resolution.
Microwave Radiometry and Remote Sensing of the Environment, 2008. MICRORAD 2008; 04/2008
[Show abstract][Hide abstract] ABSTRACT: 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 low frequency 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 vegetation, topography and convective precipitation. Other goals included supporting the development of soil moisture data sets that would contribute to understanding the role of the land surface in the concurrent North American Monsoon System. 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 (10 dates of coverage over Arizona and 11 over Sonora). Radio Frequency Interference (RFI) was observed in both PSR and satellite-based (AMSR-E) observations at 6.92 GHz over Arizona, but no detectable RFI was observed over the Sonora domain. The PSR estimated soil moisture was in agreement with the ground-based estimates of soil moisture over both domains. The estimated error over the Sonora domain (SEE = 0.021 cm3/cm3) was higher than over the Arizona domain (SEE = 0.014 cm3/cm3). These results show the possibility of estimating soil moisture in areas of moderate and heterogeneous vegetation and high topographic variability.
[Show abstract][Hide abstract] ABSTRACT: The University of Colorado (CU) Center for Environmental Technology (CET) has developed a Ground- Based Scanning Radiometer (GSR) and deployed it during two important Arctic Experiments relevant to climate research. The first was the Arctic Winter Radiometric Experiment during March-April 2004 and the second was the Radiative Heating in Underexplored Bands Campaign (RHUBC) in February-March 2007. This paper summarizes some of the design details of the instrument and gives new results from both campaigns
[Show abstract][Hide abstract] ABSTRACT: Six successful flights with the NASA P-3B aircraft over the Alaskan Arctic were conducted between March 18 and March 25, 2006 as part of the EOS Aqua AMSR-E sea ice validation efforts. The prime objective was to validate and evaluate AMSR-E snow depth on sea ice retrievals. A secondary objective was to underfly ICESat to assess the impact of snow on ICESat ice thickness retrievals. The NASA aircraft was equipped with four primary instruments: a microwave radiometer with frequencies similar to the AMSR-E, a snow depth radar, a radar altimeter, and a laser altimeter. Snow depth on sea ice validation was done in a two-step upscaling process: First, in-situ measurements of snow and sea ice along two transects were carried out over the Arctic Ocean adjacent to Barrow, AK and these measurements were overflown with the aircraft in order to validate the aircraft instruments. Subsequently, patterns over the Arctic Ocean corresponding to 4x8 12.5 km AMSR-E pixels were flown for direct comparison with the AMSR-E snow depth retrievals as well as along an ICESat track. The data set collected is probably the most comprehensive and extensive coincident set of surface- and aircraft-based ice thickness and snow depth measurements so far, and should prove useful for a variety of studies.
[Show abstract][Hide abstract] ABSTRACT: Corruption of C-band microwave brightness observations by radio-frequency interference (RFI) has been reported in recent data from orbiting radiometers; methods for mitigating these effects are of great importance for the design of future spaceborne microwave radiometers. One approach that has been suggested involves the use of multiple subchannels at C-band as opposed to a single channel; the use of multiple subchannels allows RFI to be detected and mitigated by analyzing relationships among subchannel brightnesses. While this approach has been utilized in previous airborne measurements, demonstrations of the RFI mitigation performance achieved have been difficult to obtain. To address this issue, an enhanced airborne system for observing radio-frequency interference effects on C-band microwave radiometers was developed, and is described in this paper. The system includes a traditional microwave radiometer with four C-band subchannels, so that RFI removal is possible using a subchannel mitigation algorithm. In addition, the system includes a digital receiver with the capability of providing high temporal and spectral resolution observations of interference. This high-resolution data allows improved understanding of RFI sources to be obtained, and also allows analysis of subchannel mitigation algorithm performance. Observations using the system in a test flight near Wallops Island, VA are described. Results show the four subchannel approach generally to be effective in mitigating the observed RFI sources, although examples are also illustrated using the digital receiver data to demonstrate failure of this approach. While studies of the digital receiver data alone could be performed to demonstrate further improvements in RFI mitigation, issues with this initial dataset limit the extent of such studies. Nevertheless, the results obtained still demonstrate qualitatively the improved RFI mitigation that can be achieved in brightness observations through the use of digit-
IEEE Transactions on Geoscience and Remote Sensing 08/2006; 44(7-44):1974 - 1985. DOI:10.1109/TGRS.2006.872523 · 3.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An intensive operating period (IOP) was conducted at the U. S. Department of Energy's atmospheric radiation measurement (ARM) program's field site near Barrow, Alaska, during March 9 to April 9 2004. During this IOP, radiometers were deployed over a broad frequency range (22.235 to 380 GHz), including several channels near the strong water vapor absorption line at 183.31 GHz. These radiometers were supplemented by 4-times-a-day observations by Vaisala RS90 radiosondes at the ARM Duplex in Barrow, 8 dual-radiosonde launches with "Snow White" chilled mirror radiosondes at the same location, once daily Vaisala RS90 radiosondes launched at the ARM primary field site, and twice-daily synoptic launches by the US National Weather Service. Radiometers deployed included the ground-based scanning radiometer of NOAA (several frequencies from 50 to 380 GHz), the microwave radiometer and the radiometric profiler of ARM (frequencies from 22.235 to 60 GHz), and a global positioning system operated by NOAA. In addition, all of the ARM active cloud sensors were operated. Selected results from this experiment are presented, including observed radiometric sensitivities to precipitable water vapor and liquid water path, radiosonde comparisons between radiosondes types and to MWRP measurements, and a preliminary comparison of forward models with GSR data
[Show abstract][Hide abstract] ABSTRACT: The Polarimetric Scanning Radiometer (PSR/CX) was flown on a P-3B aircraft as part of SMEX04. PSR/CX has been successfully operated during several previous airborne campaigns. The primary objectives of PSR/CX during SMEX04 are: 1) Contribute to the calibration and validation of AMSR observations over different parts of the globe and to check for the presence of Radio Frequency Interference (RFI), 2) Explore the potential for the development of soil moisture retrieval algorithms using C-band imagery in diverse landscapes (Arizona and Sonora, Mexico), and 3) to develop retrieval algorithms to estimate soil moisture over areas of topographic variability and vegetation. The dominant landuse classes in the different SMEX04 domains are: 1) Arizona - semi-arid climate with sparse vegetation and moderate topography, and 2) Sonora, Mexico - moderate vegetation with strong topographic gradients. SMEX04 consisted of about 84 flightlines at high altitude resulting in 21 mapping domains flown during August, 2004 (11 over Arizona and 10 over Sonora). Each mapping domain is about 75 km x 50 km, providing an excellent area for calibration and validation of AMSR-E observations. Some areas of the SMEX04 domain received heavy localized precipitation as a result of convective activity during the experiment. These resulted in interesting brightness temperature patterns with strong brightness temperature gradients. The presence of these diverse conditions will help address questions relating to scaling of spaceborne microwave observations. Results of comparison between PSR and AMSR and the use of microwave remote sensing to estimate soil moisture over wide range of vegetation and soil moisture conditions are also presented.
[Show abstract][Hide abstract] ABSTRACT: The 2004 Arctic Winter Radiometric Experiment was conducted at the North Slope of Alaska (NSA) Atmospheric Radiation Measurement (ARM) Program field site near Barrow, Alaska from March 9 to April 9, 2004. The goals of the experiment were: to study the microwave and millimeter wave radiometric response to water vapor and clouds during cold and dry conditions; to obtain data for forward model studies at frequencies ranging from 22.235 to 400 GHz, to demonstrate new Environmental Technology Laboratory's (ETL) radiometric receiver and calibration technology and to compare both radiometric and in situ measurements of water vapor.
[Show abstract][Hide abstract] ABSTRACT: One of the main goals of the NASA Cold Land Processes Experiment is to explore scaling issues associated with microwave remote sensing of snow-packs. During the experiment, microwave radiometer observations were made at scales from the plot scale up to satellite pixels (25x25 Km2). In this paper, brightness temperatures acquired by the University of Tokyo's Ground Based Microwave Radiometer-7 (GBMR-7), the NOAA Polarimetric Scanning Radiometer (PSR/A), the SSM/I and AMSR-E satellite radiometers during the third Intensive Observation Period (IOP3, dry snow, February 19 - 25, 2003) have been analyzed and compared. Differences among observations are discussed. The effects of topography, as well as different antenna footprint positions, observation times and calibrations are considered and used to understand the differences observed at the different scales. In addition, inter-satellite differences were observed.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: The NASA Cold-land Processes Field Experiment-1 (CLPX-1) involved several instruments in order to acquire data at different spatial resolutions. Indeed, one of the main tasks of CLPX-1 was to explore scaling issues associated with microwave remote sensing of snowpacks. To achieve this task, microwave brightness temperatures collected at 18.7, 36.5, and 89 GHz at LSOS test site by means of the University of Tokyo's Ground Based Microwave Radiometer-7 (GBMR-7) were compared with brightness temperatures recorded by the NOAA Polarimetric Scanning Radiometer (PSR/A) and by SSM/I and AMSR-E radiometers. Differences between different scales observations were observed and they may be due to the topography of the terrain and to observed footprints. In the case of satellite and airborne data, indeed, it is necessary to consider the heterogeneity of the terrain and the presence of trees inside the observed scene becomes a very important factor. Also when comparing data acquired only by the two satellites, differences were found. Different acquisition times and footprint positions, together with different calibration and validation procedures, can be responsible for the observed differences.
[Show abstract][Hide abstract] ABSTRACT: An airborne system for observing radio frequency interference at C-band is described. The digital receiver included has the capability of providing high temporal and spectral resolution of interference, as well as implementing simple mitigation strategies. Plans for observations with the system are discussed.
[Show abstract][Hide abstract] ABSTRACT: During March 2003, an extensive field campaign was conducted near Barrow, Alaska to validate AQUA Advanced Microwave Scanning Radiometer (AMSR) sea ice products. Field, airborne and satellite data were collected over three different types of sea ice: 1) first year ice with little deformation, 2) first year ice with various amounts of deformation and 3) mixed first year ice and multi-year ice with various degrees of deformation. The validation plan relies primarily on comparisons between satellite, aircraft flights and ground-based measurements. Although these efforts are important, key aspects such as the effects of atmospheric conditions, snow properties, surface roughness, melt processes, etc on the sea ice algorithms are not sufficiently well understood or documented. To improve our understanding of these effects, we combined the detailed, in-situ data collection from the 2003 field campaign with radiance modeling using a radiative transfer model to simulate the top of the atmosphere AMSR brightness temperatures. This study reports on the results of the simulations for a variety of snow and ice types and compares the results with the National Oceanographic and Atmospheric Administration Environmental Technology Laboratory Polarimetric Scanning Radiometer (NOAA) (ETL) (PSR) microwave radiometer that was flown on the NASA P-3.