Vladimir Ye. Leuski

Measurement of Low Amounts of Precipitable Water Vapor Using Ground-Based Millimeterwave Radiometry

Abstract Extremely dry conditions characterized by amounts of precipitable water vapor (PWV) as low as 1–2 mm commonly occur in high-latitude regions during the winter months. While such dry atmospheres carry only a few percent of the latent heat energy compared to tropical atmospheres, the effects of low vapor amounts on the polar radiation budget—both directly through modulation of longwave radiation and indirectly through the formation of clouds—are considerable. Accurate measurements of PWV during such dry conditions are needed to improve polar radiation models for use in understanding and predicting change in the climatically sensitive polar regions. To this end, the strong water-vapor absorption line at 183.310 GHz provides a unique means of measuring low amounts of PWV. Weighting function analysis, forward model calculations based upon a 7-yr radiosonde dataset, and retrieval simulations consistently predict that radiometric measurements made using several millimeter-wavelength (MMW) channels near ...

Airborne radio-frequency interference studies at C-band using a digital receiver

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 digital receivers

The Ground-Based Scanning Radiometer: A Powerful Tool for Study of the Arctic Atmosphere

Measurements of water vapor and clouds in the polar regions are difficult, because conventional instruments show little sensitivity (~1.3 K/mm) to low amounts. On the other hand, millimeter- and submillimeter-wavelength radiometry offers greatly enhanced sensitivity (up to 51.4 K/mm, depending upon frequency). For this reason, the National Oceanic and Atmospheric Administrations Physical Science Division designed a new instrument, the Ground-Based Scanning Radiometer (GSR), for continuous and unattended observations at millimeter and submillimeter wavelengths (50-380 GHz). The GSR was deployed for the first time during the Arctic winter radiometric experiment in March-April 2004. In this paper, we discuss the GSR calibration procedure, which allows for accurate measurements during clear and cloudy skies. Error-budget analysis and comparison with independent measurements show an absolute accuracy on the order of 1-2 K. Examples of multifrequency and multiangle GSR observations are illustrated, representing a valuable new data set for the study of water vapor, clouds, and atmospheric absorption models in the Arctic.

Air and sea surface temperature measurements using a 60-GHz microwave rotating radiometer

Data obtained from a single-channel scanning 5 mm radiometer on a research vessel were used for the study of sea surface temperature and lower-atmospheric temperature; profiles under neutral, weakly stable, and unstable conditions. Comparisons with in situ air and water temperature measurements, dropsonde temperature data, radiosonde data, and VV Ku-band side-looking radar images are presented. The technique based on 5-mm measurements determines the air-skin water (skin depth of 0.3 mm) temperature difference with an accuracy of the order of 0.1 K. Analysis of the experimental data suggests that the air-skin water temperature difference depends weakly on solar heating and wind speed V for 2.5

Microwave and Millimeter-Wave Radiometric and Radiosonde Observations in an Arctic Environment

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 significant 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 radio...

On-board accurate calibration of dual-channel radiometers using internal and external references

This paper presents a method for combining internal noise injection and external reference standard looks to accurately calibrate an airborne dual-channel radiometer. The method allows real-time estimation of the correct values of the radiometer gains and offsets, even for nontemperature-stabilized radiometers and with minimum loss of measurement time spent in external load measurement. Crosstalk and leakage introduced by the noise injection circuitry is also taken into account, thus providing high gain and offset estimation accuracy. The method was implemented on a National Oceanic and Atmospheric Administration airborne instrument, the Polarimetric Scanning Radiometer, which was used to obtain an extensive set of radiometric measurements over oceanic convection during CAMEX3 in August-September 1998.

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.

Ground-Based Millimeter- and Submillimiter Wave Observations of the Arctic Atmosphere

Ground-based millimeter(mm)- and submillimeter (submm)-wave observations were collected during the Arctic winter by a new 25-channel scanning radiometer. Theoretical analysis and observations are shown to demonstrate the enhanced sensitivity of mm- and submm-wave radiometers with respect to conventional instruments, such microwave radiometers and global positioning system, to small changes in water vapor and liquid at low contents. A quantitative analysis of mm- and submm-wavelength sensitivity was carried out, yielding factors from 1.5 to 69 (3 to 4) for integrated water vapor (liquid water) content when compared to 20-30 GHz radiometers. A weighting function analysis illustrates the capability to retrieve atmospheric temperature, humidity, and liquid path from ground-based scanning radiometer (GSR) observations in the extreme conditions of the Arctic winter. Finally, we show preliminary results for the retrievals, and we discuss the path of the future research

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.