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A 1-D 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-wavelengths. The GSR was deployed in two Arctic experiments held at the Atmospheric Radiation Measurement Program in Barrow, Alaska. Temperature and humidity profiles retrieved with the 1DVAR technique are compared with simultaneous radiosonde observations (RAOBs) during the Radiative Heating in Underexplored Bands Campaign (February-March 2007). Examples and statistical results are presented and discussed to demonstrate the achieved retrieval accuracy and vertical resolution. The 1DVAR retrievals based on GSR observations improve the NWP background up to 5 km, particularly in the lower 3 km. The present implementation achieved an root-mean-square (rms) error with respect to RAOB within 1.5 K for temperature and 0.10 g/kg for humidity profiles of up to 5 km in height, with 2.9 and 2.0 degrees of freedom for signal, respectively. Using the interlevel covariance definition of the vertical resolution, the 1DVAR retrievals showed a < 1-km vertical resolution of up to 5 km for both temperature and humidity profiles. The integrated water vapor obtained from the retrieved humidity profiles showed an rms accuracy within 0.10 kg/m², with small bias (< 0.01 kg/m²) and excellent correlation (0.96). [ABSTRACT FROM AUTHOR]

A 1-D 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-wavelengths. The GSR was deployed in two Arctic experiments held at the Atmospheric Radiation Measurement Program in Barrow, Alaska. Temperature and humidity profiles retrieved with the 1DVAR technique are compared with simultaneous radiosonde observations (RAOBs) during the Radiative Heating in Underexplored Bands Campaign (February-March 2007). Examples and statistical results are presented and discussed to demonstrate the achieved retrieval accuracy and vertical resolution. The 1DVAR retrievals based on GSR observations improve the NWP background up to 5 km, particularly in the lower 3 km. The present implementation achieved an root-mean-square (rms) error with respect to RAOB within 1.5 K for temperature and 0.10 g/kg for humidity profiles of up to 5 km in height, with 2.9 and 2.0 degrees of freedom for signal, respectively. Using the interlevel covariance definition of the vertical resolution, the 1DVAR retrievals showed a < 1-km vertical resolution of up to 5 km for both temperature and humidity profiles. The integrated water vapor obtained from the retrieved humidity profiles showed an rms accuracy within 0.10 kg/m², with small bias (< 0.01 kg/m²) and excellent correlation (0.96). [ABSTRACT FROM AUTHOR]

During the Radiative Heating in Underexplored Bands Campaign (RHUBC), held in February-March 2007, three millimeter-wave radiometers were operated at the Atmospheric Radiation Measurement Program's site in Barrow, Alaska. These radiometers contain several channels located around the strong 183.31-GHz water vapor line, which is crucial for ground-based water-vapor measurements in very dry conditions, typical of the Arctic. Simultaneous radiosonde observations were carried out during conditions with very low integrated-water-vapor (IWV) content (< 2mm). Observations from the three instruments are compared, accounting for their different design characteristics. The overall agreement during RHUBC among the three instruments and between instruments and forward model is discussed quantitatively. In general, the instrument cross-validation performed for sets of channel pairs showed agreement within the total expected uncertainty. The consistency between instruments allows the determination of the IWV to within around 2% for these dry conditions. Comparisons between these data sets and forward-model simulations using radiosondes as input show spectral features in the brightness-temperature residuals, indicating some degree of inconsistency between the instruments and the forward model. The most likely cause of forward-model error is systematic errors in the radiosonde humidity profiles. [ABSTRACT FROM AUTHOR]

The article discusses the highlights of the 10th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment (MicroRad'08) held in Florence, Italy from March 11 to 14, 2008. The opening speech by organizer Paolo Pampaloni was dedicated in memory of Professor Giovanni d'Auria of the University of Rome in Italy. A session on the Advanced Microwave Scanning Radiometer (AMSR) for Earth Observing System (EOS) was conducted. The meeting ended with a wine and cheese reception.

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 Administration's 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. [ABSTRACT FROM AUTHOR]

Brightness temperatures computed from five absorption models and radiosonde observations were analyzed by comparing them with measurements from three microwave radiometers at 23.8 and 31.4 6Hz. Data were obtained during the Cloudiness Inter-Comparison Experiment at the U.S. Department of Energy's Atmospheric Radiation Measurement Program's (ARM) site in North-Central Oklahoma in 2003. The radiometers were calibrated using two procedures, the so-called instantaneous "tipcal" method and an automatic self-calibration algorithm. Measurements from the radiometers were in agreement, with less than a 0.4-K rms difference during clear skies, when the instantaneous method was applied. Brightness temperatures from the radiometer and the radiosonde showed a bias difference of less than 0.69 K when the most recent absorption models were considered. Precipitable water vapor (PWV) computed from the radiometers were also compared to the PWV derived from a Global Positioning System station that operates at the ARM site. The instruments agree to within 0.1 cm in PWV retrieval. [ABSTRACT FROM AUTHOR]

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 the 183-GHz line, together with established microwave (MW) measurements near the 22.235-GHz water-vapor line and ∼31-GHz atmospheric absorption window can be used to determine within 5% uncertainty the full range of PWV expected in the Arctic. This combined capability stands in spite of accuracy limitations stemming from uncertainties due to the sensitivity of the vertical distribution of temperature and water vapor at MMW channels. In this study the potential of MMW radiometry using the 183-GHz line for measuring low amounts of PWV is demonstrated both theoretically and experimentally. The study uses data obtained during March 1999 as part of an experiment conducted at the Department of Energy’s Cloud and Radiation Testbed (CART) site near Barrow, Alaska. Several radiometers from both NOAA and NASA were deployed during the experiment to provide the first combined MMW and MW ground-based dataset during dry Arctic conditions. Single-channel retrievals of PWV were performed using the MW and MMW data. Discrepancies in the retrieved values were found to be consistent with differences observed between measured brightness temperatures (TBs) and forward-modeled TBs based on concurrent radiosonde profiles. These discrepancies are greater than can be explained by radiometer measurement error alone; errors in the absorption models and uncertainty in the radiosonde measurements contribute to the discrepancies observed. The measurements, retrieval technique, and line model discrepancies are discussed, along with difficulties and potential of MMW/MW PWV measurement. [ABSTRACT FROM AUTHOR]

We discuss the performances of a set of four microwave water vapor radiometers operating in the 20-30-GHz band during a field experiment, with an emphasis on calibration and achievable accuracy. The field experiment was conducted at the Department of Energy's Atmospheric Radiation Measurement Program's field site in north central Oklahoma, and was focused on clear-sky water vapor measurements by both radiometers and radiosondes. A comparison between two published radiometric tip curve calibration procedures is presented, and these procedures are applied to measurements from two nearly identical instruments placed a few meters apart. Using the instantaneous tip cal method of the Environmental Technology Laboratory, the brightness temperature measurements for the two identical instruments differed by less than 0.2 K over a 24-h period. Results from reference load cryogenic tests and brightness temperature cross comparisons have shown differences within 0.7 K. In addition, we compare radiometric measurements with calculations of brightness temperature based on the Rosenkranz absorption model and radiosonde observations. During the experiment, both Vaisala-type RS80 and RS90 humidity sensors were used. Our comparisons demonstrate the improvements achieved by the new Valsala RS90 sensors in atmospheric humidity profiling, which reduce or eliminate the "dry bias" problem. [ABSTRACT FROM AUTHOR]

Presents a data simulation approach to isolate and analyze influential factors in the calibration processes. Techniques to reduce calibrating uncertainties; Details on radiative transfer and radiometer equations; Tipping calibration method; Conclusion.

Presents a study which focuses on sea surface temperature and lower-atmospheric temperature profiles with reference to the use of data from a single-channel scanning radiometer. What the technique determines; Suggestion from the analysis of the experimental data; Information on a turbulent heat transfer at the surface.

Hans Joachim Liebe, an internationally recognized expert in radiowave physics, and developer of the widely-used Millimeter-wave Propagation Model (MPM), passed away peacefully on August 2, 2012, after a long and courageous battle with Parkinson's disease. He was the son of Margarete and Fritz Liebe, and was born in Insterburg, East Prussia, Germany, on January 21, 1934. He married Roswita Borgwardt in 1963, and they were married 49 years. In 1964, he graduated magna cum laude from the Technical University of Berlin, where he earned the PhD in Electrical Engineering. In 1965, he moved from Germany to the United States with his family. [ABSTRACT FROM AUTHOR]