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All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Performance appraisal of VAS radiometry for GOES-4, -5 and -6

The first three VISSR Atmospheric Sounders (VAS) were launched on GOES-4, -5, and -6 in 1980, 1981 and 1983. Postlaunch radiometric performance is assessed for noise, biases, registration and reliability, with special attention to calibration and problems in the data processing chain. The postlaunch performance of the VAS radiometer meets its prelaunch design specifications, particularly those related to image formation and noise reduction. The best instrument is carried on GOES-5, currently operational as GOES-EAST. Single sample noise is lower than expected, especially for the small longwave and large shortwave detectors. Detector to detector offsets are correctable to within the resolution limits of the instrument. Truncation, zero point and droop errors are insignificant. Absolute calibration errors, estimated from HIRS and from radiation transfer calculations, indicate moderate, but stable biases. Relative calibration errors from scanline to scanline are noticeable, but meet sounding requirements for temporarily and spatially averaged sounding fields of view. The VAS instrument is a potentially useful radiometer for mesoscale sounding operations. Image quality is very good. Soundings derived from quality controlled data meet prelaunch requirements when calculated with noise and bias resistant algorithms.

Chesters, D.↗
NASA NTRS1983

Use of VAS multispectral data for sea surface temperature determination

The Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) is a radiometer possessing eight visible channel detectors and six thermal detectors that sense infrared radiation in 12 spectral bands. Housed in the GOES satellite, VAS spins in a west to east direction at 100 rpm and achieves spatial coverage at resolutions of 1 km in the visible and 7 or 14 km in the infrared by stepping a scan mirror in a north to south direction. Designed for multipurpose applications, the VAS can be operated in two different modes: (1) a multi-spectral imaging (MSI) mode, and (2) a dwell sounding (DS) mode. The MSI mode of operation is used for sea surface temperature (SST) determination. Currently, a full-disk MSI image for SST determination is received every hour, 18 hours a day during weekdays. This MSI mode of operation for SST consists of data obtained from wavelengths centered at 3.9 microns (channel 12), 11.6 microns (channel 8), and 12.6 microns (channel 7) as well as visible data.

Bates, J.↗
NASA NTRS1984

Regional scale simulation of atmospheric structure using VAS data

Investigations with both Subsynoptic Scale Model (SSM) and Limited Area Mesoscale Prediction System (LAMPS) are directed at model static initializations using Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) derived temperatures and moistures and also satellite derived winds. The general approach for each day's case study is similar. A 12-hour control forecast (no satellite data) is made 12Z-OZ, using a radiosonde analysis at 12Z as the initial field. For the satellite data experiments, reanalyses are performed at intermediate times, using VAS soundings or VAS soundings in combination with satellite winds. Forecasts are subsequently made from the reanalysis time(s) to the same validation hour (OZ) as the control forecasts. Comparisons are then made between the control forecast and satellite experiments.

Disk, G.↗
NASA NTRS1984

Mesoscale analysis of VAS 6.7 micron image data for several case studies

Several case studies are examined in an attempt to relate Visible infrared spin scan radiometers Atmospheric Sounder (VAS) water vapor channel radiance data to atmospheric moisture. Since the 6.7 micrometer channel detects radiation emitted by atmospheric water vapor from a rather thick layer, a scheme is developed which weighted rawinsonde observations of relative humidity in a similar manner. A comparison of the two fields (weighted relative humidity values from gridded rawinsonde observations and the VAS water vapor image) indicates that even when mesoscale data are used, the technique only presented a smooth representation of the radiance field. This weighting function is dependent on both the temperature and moisture distribution of the atmosphere. Cross sections of relative humidity from the mesoscale rawinsondes are produced which sliced the water vapor imagery in particularly interesting regions (areas of high and low blackbody temperatures). Comparisons are then made between the cross sections and the variations in the VAS radiance data along the cross section line. Bright regions in the water vapor imagery (cold blackbody temperatures) are often associated with thin layers of high relative humidity or thick layers of only moderately moist air. The reverse also applies, i.e., dark regions (warm blackbody temperatures) in the imagery corresponded well with very dry regions in the cross sections.

Jedlovec, G. J.↗
NASA NTRS1984

Statistical severe storm nowcasting comparison of VAS and Rawinsonde soundings

The statistical severe storm nowcasting technique using upper air soundings (VAS or radiosonde) is translated to the IBM McIDAS system. The severe storm information content of Visible infrared spin scan radiometer Atmospheric Sounder (VAS) and rawinsonde sounding data is compared. The contours of the likelihood of severe storms based only upon upper air VAS and rawinsonde data are shown, as well as the outlook based upon surface data, radar, operational computer models, and other data sources.

Keller, D. L.↗
NASA NTRS1984

NSSFC: VAS assessment activities

Vertical atmospheric sounder data were evaluated. Basic work thus far has been directed toward evaluating, over the in near real time to determine the instrument's ability to detect regions with potential for severe storm development. A real time hourly water vapor loop 16 hours daily provides data to monitor position and trends of mid and upper level meteorological features. Because water vapor is more uniform than clouds, the water vapor images improve the ability to monitor certain atmospheric features such as jets, shortwaves, vorticity centers, and subsidence zones. Additional products to be evaluated include a version of the split window developed by NASA and cloud drift winds generated from three hourly sequenced CO2 VAS channels. A technique also under evaluation at NSSFC provides hail size potential based on VAS sounding data. Part of a planned upgrade to CSIS linking the 9600 baud phone line to one of the CSIS CPUs to allow access to VAS data via CSIS.

Anthony, R. W.↗
NASA NTRS1984

Applications of VAS and TOVS to tropical cyclones

The results of the attempts to use VAS (visible IR spin scan radiometer atmospheric sounder) data for predicting tropical cyclones are reported. VAS, mounted on a GEO platform, has 14 detectors for upwelling radiance. The McIDAS software was, by the 1983 hurricane season, upgraded to providing imagery and mass, motion and moisture patterns using the satellite data, which also permitted determinations of accurate temperature and moisture profiles. Comparisons made between VAS and radiosonde data revealed fairly close agreement of satellite and in-situ conditions during the 1983 season. When combined with data from the Tiros operational vertical sounder (TOVS) to define wind streamlines and predict the path of a hurricane from data fed into numerical models, sufficiently good agreement was obtained to initiate plans to forecast a hurricane trajectory during the 1984 season.

Velden, C. S.↗
NASA NTRS1984

Delineating mid- and low-level water vapor patterns in pre-convective environments using VAS moisture channels

Infrared and visible imagery from VAS are used to delineate mid- and lower-tropospheric moisture fields for a variety of severe storm cases in the southern and central United States. The ability of sequences of images to isolate areas of large negative vertical moisture gradients and apparent convective instability prior to the onset of convective storms is assessed. A variety of image combination procedures are used to deduce the stability fields which are then compared with the available radiosonde data. The results for several severe storm cases indicate that VAS can detect mid- and low-level mesoscale water vapor fields as distinct radiometric signals. The VAS imagery shows a strong tendency for thunderstorms to develop along the edges of bands of midlevel dryness as they overtake either preexisting or developing low-level moisture maxima. Image sequences depict the speed with which deep moist and dry layers can develop and move.

Petersen, R. A.↗
NASA NTRS1985

Hurricane Debby - An illustration of the complementary nature of VAS soundings and cloud and water vapor motion winds

The utility of VISSR Atmospheric Sounder (VAS) temperature and moisture soundings and cloud and water vapor motion winds in defining a storm and its surroundings at subsynoptic scales has been examined using a numerical analysis and prognosis system. It is shown that the VAS temperature and moisture data, which specify temperature and moisture well in cloud-free areas, are complemented by cloud and water vapor motion data generated in the cloudy areas. The cloud and water vapor 'winds' provide thermal gradient information for interpolating the soundings across cloudy regions. The loss of analysis integrity due to the reduction of VAS sounding density in the cloudy regions associated with synoptic activity is ameliorated by using cloud and water vapor motion winds. The improvement in numerical forecasts resulting from the addition of these data to the numerical analysis is recorded.

Le Marshall, J. F.↗
NASA NTRS1984

A statistical evaluation and comparison of VISSR Atmospheric Sounder (VAS) data and corresponding rawinsonde measurements

The mesoscale accuracy of GOES Visible/IR Spin-Scan-Radiometer (VISSR) Atmospheric Sounder (VAS) temperature profiles and mean-precipitable-water measurements obtained over central Texas on March 6, 1982, is evaluated on the basis of comparing them with three-hourly rawinsonde data (up to 100 mbar) of similar spatial resolution for the same area and time. The VAS data comprise three sets: physical retrievals by the method of Smith (1970), modified physical retrievals by the method of Smith (1983), and regression soundings (incorporating some rawinsonde data) by the method of Lee et al. (1983). The data are presented graphically, and all three VAS data sets are found to have similar temperature biases, which vary from hot to cold with altitude and are apparently related to major inversions. Systematic moisture biases are seen in the physical and modified physical data sets, while the regression soundings are relatively unbiased but do not accurately reproduce moisture gradients seen in the rawinsonde data.

Jedlovec, G. J.↗
NASA NTRS1984

Mesoscale analysis of 6.7 micron image data from the VISSR Atmospheric Sounder (VAS) for several case studies

Several case studies are examined in an attempt to relate Visible infrared spin scan radiometers Atmospheric Sounder (VAS) water vapor channel radiance data to atmospheric moisture. Since the 6.7 micrometer channel detects radiation emitted by atmospheric water vapor from a rather thick layer, a scheme is developed which weighted rawinsonde observations of relative humidity in a similar manner. A comparison of the two fields (weighted relative humidity values from gridded rawinsonde observations and the VAS water vapor image) indicates that even when mesoscale data are used, the technique only presented a smooth representation of the radiance field. This weighting function is dependent on both the temperature and moisture distribution of the atmosphere. Cross sections of relative humidity from the mesoscale rawinsondes are produced which sliced the water vapor imagery in particularly interesting regions (areas of high and low blackbody temperatures). Comparisons are then made between the cross sections and the variations in the VAS radiance data along the cross section line. Bright regions in the water vapor imagery (cold blackbody temperatures) are often associated with thin layers of high relative humidity or thick layers of only moderately moist air. The reverse also applies, i.e., dark regions (warm blackbody temperatures) in the imagery corresponded well with very dry regions in the cross sections.

Jedlovec, G. J.↗
NASA NTRS1986

Optimized retrievals of precipitable water fields from combinations of VAS satellite and conventional surface observations

VISSR (visible and infrared spin-scan radiometer) atmospheric sounder (VAS) radiances and conventional surface temperature and dewpoint data are used in several combinations within a regression approach to determine the optimum resolution and accuracy of precipitable water (PW) fields retrieved from satellite observations. Point retrievals at radiosonde stations are used to determine the numerical accuracy of each retrieval technique, and image sequences of the retrieved PW fields are used to determine the temporal stability and spatial coherence of mesoscale PW features. VAS channels 5, 6, 7, and 8 and the surface dewpoint contribute the most information to regression-based retrievals of PW. The most accurate PW retrievals are obtained when radiances are averaged to a resolution of 15 to 60 km. A physical 'split-window' approach provides better PW estimates than regression when only the 11- and 12-micron VAS channels are available or when radiosonde-based training is limited to only one time period.

Robinson, W. D.↗
NASA NTRS1985

Statistical analysis and use of VAS radiance data

Researchers goals are to describe the information content of Vertical Atmospheric Sounder (VAS) radiance data, especially the 6.7 micrometers water vapor channel, to better interpret the atmosphere's water vapor structure from 6.7 micrometers imagery, and to investigate new analysis and forecasting techniques utilizing retrieved VAS soundings. Researchers made major progress toward these goals during FY-85. They are investigating 6.7 micrometer imagery on 6 to 7 March 1982, a day when special mesoscale ground truth data were collected during the 1982 atmospheric variability experiment/vertical amospheric sounder (AVE/VAS) field experiment. A dark (dry) image streak having mesoscale details was located over the special data region, and it provides the major focus of the case study. Mesoscale radiosonde-derived humidity data are found to verify fine scale features of the image that are not evident from the standard National Weather Service network. Thus, VAS imagery is a reliable detector of mesoscale moisture structure during this case. To investigate causes for the image streak, researchers are calculating water vapor budgets. Subsidence is found to be a factor in the current case as well; however, patterns of descent are not related to the jet streak according to traditional conceptual models. Thus, it appears that more research into jet stream dynamics is needed in order to better interpret 6.7 micrometer imagery.

Fuelberg, H. E.↗
NASA NTRS1986

Utilization of VAS satellite data in the initialization of an oceanic-cyclogenesis simulation

A series of experiments was performed to test various method of incorporating Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS)-sounding data into the initial conditions of the Penn State University/National Center for Atmospheric mesoscale model. The VAS data for this ocean-cyclogenesis case consist of 110 irregularly distributed temperature and humidity soundings located over the North Pacific Ocean and apply at approximately 1200 GMT 10 November 1981. Various methods of utilizing VAS data in the initial condition of a mesoscale model were evaluated.

Douglas, Sharon G.↗
NASA NTRS1986

Optimum retrieval of precipitable water fields from VAS and surface data

The use of VAS radiances and conventional surface data to determine the optimum resolution and accuracy of low-level precipitable water fields retrieved from geosynchronous satellite observations is examined. VAS retrievals of precipitated water (PW) are compared with various channel selections in the regression algorithm and with the split window algorithm. The split window algorithm and the linear regression algorithm are described. Consideration is given to the sounding-field-of-view (SFOV) resolution; the data reveal that the optimum resolution for the split window algorithm is at 15-60 km resolution, and 30-60 km SFOV resolution is optimal for the regression method. Statistics and images from PW retrieval experiments conducted on July 13, 1981 are presented and utilized to determine optimum channel selection. A fast contouring method for VAS sounding images is proposed.

Chesters, Dennis↗
NASA NTRS1986

Verification of small-scale water vapor features in VAS imagery using high resolution MAMS imagery

The Multispectral Atmospheric Mapping Sensor (MAMS), a modification of NASA's Airborne Thematic Mapper, is described, and radiances from the MAMS and the VISSR Atmospheric Sounder (VAS) are compared which were collected simultaneously on May 18, 1985. Thermal emission from the earth atmosphere system in eight visible and three infrared spectral bands (12.3, 11.2 and 6.5 microns) are measured by the MAMS at up to 50 m horizontal resolution, and the infrared bands are similar to three of the VAS infrared bands. Similar radiometric performance was found for the two systems, though the MAMS showed somewhat less attenuation from water vapor than VAS because its spectral bands are shifted to shorter wavelengths away from the absorption band center.

Menzel, Paul W.↗
NASA NTRS1987

Assimilation of scalar versus horizontal gradient information from the VAS into a mesoscale model

Comparisons are made between analyses and forecasts which incorporate VAS geopotential data as either scalar or horizontal gradient information for a case study on the AVE/VAS day of Mar. 6, 1982. On this day, incorporating the VAS information in analysis as a variational constraint on horizontal geopotential gradients significantly mitigated the effects of large data biases which made VAS assimilation by standard scalar methods very difficult. A subsequent forecast made from the gradient assimilation was superior to one made from the standard analysis and of comparable quality in geopotentials to a control forecast from synoptic data. Most impact was noted in the forecasts of vertical motion and precipitation in the gradient vs this control simulation.

Diak, George↗
NASA NTRS1987

An evaluation of various forms of VAS retrievals in the analysis of a preconvective environment

VISSR Atmospheric Sounder (VAS) radiance data obtained over the continental United States on July 20, 1981 are used to evaluate a variety of VAS retrieval procedures and parameters in the qualitative analysis and forecasting of severe weather events. The particular case analyzed contains two significantly different mesoscale convective events in the central plains. Retrievals of temperature, dewpoint temperature, equivalent potential temperature, total column precipitable water, and lifted index are shown to be physically consistent in space and time and to compare well with available radiosonde data. The analysis of the VAS retrievals identified significant spatial gradients and temporal changes in the thermal and moisture fields, including times and locations between radiosonde observations.

Petersen, R. A.↗