VISSR Atmospheric Sounder Research Articles

Coupled Assimilation of Geostationary Satellite Sounder Data into a Mesoscale Model Using the Bratseth Analysis Approach

Abstract A satellite–model coupled procedure for assimilating geostationary satellite sounder data was adapted to a mesoscale analysis and forecast system jointly developed by the Naval Research Laboratory and the Air Force Research Laboratory. The coupled procedure involves the use of the model output fields as the first guess for the thermodynamic retrievals. Atmospheric thermodynamic profiles and ground temperatures were retrieved from observed radiances of the VISSR Atmospheric Sounder (VAS) on board the Geostationary Operational Environmental Satellite. The successive corrections objective analysis scheme in the mesoscale analysis and forecast system was modified to consider the horizontal spatial correlation of the satellite data. The procedure was tested using a wintertime case from the 1986 Genesis of Atlantic Lows Experiment project. The retrievals generated by the coupled method were modestly improved relative to independent stand-alone retrievals. Coupled analyses and forecasts of temperature a...

Simulation of remote sensing of sea surface temperature from space: influences of cirrus clouds and stratospheric aerosols on sea surface temperatures derived from the VISSR Atmospheric Sounder

Abstract This simulation study demonstrates that cirrus clouds and volcanic aerosols with atmospheric gases would greatly affect the transmission functions and brightness temperatures of infrared window channels in the VISSR Atmospheric Sounder (VAS), and VAS-derived sea surface temperature (SST) determinations. The ;clear air (CLR) retrieval equations should not be used in the presence of cirrus and high stratospheric aerosol loadings. An alternative five-window channel algorithm could be found that would work in arbitrary clear, cirrus or aerosol conditions, but the retrieval accuracy would decrease in comparison with the multi-channel SST (MCSST) algorithms for simply cirrus clouds, or aerosols only. In MCSST algorithms, channel 12 (3–94μ) is most important for CLR, or tenuous cirrus with any kind of aerosols, or moderate cirrus with weak aerosols, whereas for moderate cirrus combined with the strong aerosol, or dense cirrus with any kind of aerosols, channel 5 (13‐34μ) or channel 8 (11–22μ) becomes the most important. In addition, the effects of variations of water vapour profile, aerosol concentration, and sea surface reflection (SSR) on SST retrievals need to be considered.

A satellite‐based estimate of evapotranspiration over Amazonia

Abstract If rainfall, storage and flux divergence are known, evapotranspiration can be estimated as the residual in a budget of atmospheric moisture. We describe a new approach to moisture‐budget estimates of Amazon evapotranspiration. Synoptic observations (and numerical model analyses from the U.S. National Meteorological Center) are combined with wind, humidity and rain information retrieved from radiances measured by the Geostationary Operational Environmental Satellite (GOES). Rainfall is inferred from the thermal infrared channel of the Visible and Infrared Spin Scan Radiometer (VISSR). Humidity is retrieved from the VISSR Atmospheric Sounder (VAS). Winds are inferred from both VISSR and VAS images, using visible, thermal infrared and water vapor bands. Satellite and station or model information is merged by means of a recursive filter. The GOES‐budget approach was tested over a three‐day period from May 1987. Our estimate of evapotranspiration over the basin, 9 mm/d, is unrealistically large. A sen...

A Technique for Deriving Column-integrated Water Content Using VAS Split-Window Data

An algorithm is examined that uses VISSR Atmospheric Sounder (VAS) 11- and 12-micron (split-window) data to derive column-integrated water content (IWC) at mesoscale resolution. The algorithm is physically based and derives its first-guess information from radiosonde data. The procedure is applied first to a test case data set and then to the 19 June 1986 study day from the Cooperative Huntsville Meteorological Experiment (COHMEX). Ground truth data for verifying results from the technique include IWC from National Weather Service and COHMEX radiosondes, the Multispectral Atmospheric Mapping Sensor (MAMS), and a special set of VAS soundings (12 channel) using an independent retrieval method. Results from the test case show reasonable accuracy with the rms errors as low as +/- 3.8 mm. On the 19 June case study day IWC analyses depict reasonable gradients and exhibit good spatial and temporal continuity. Furthermore, they provide insight into preferred regions for cumulus cloud and thunderstorm formation. On the average, a mean absolute retrieval error of 2.4 mm (an 8.1 percent error) and a rms error of +/- 2.9 mm are obtained on the case study day. These results compare favorably with those from existing VAS IWC techniques. Overall, the findings indicate that the technique has excellent potential to depict mesoscale moisture variations.

High resolution depiction of atmospheric moisture, stability and surface temperature from combined MAMS and VAS radiances

In order to elucidate mesoscale variability of the earth-atmosphere system, aircraft-borne Multi-spectral Atmospheric Mapping Sensor (MAMS), 100-meter-resolution radiometric data, and geostationary-borne VISSR Atmospheric Sounder (VAS) 8-km-resolution radiometric data are used together in a physical retrieval method to produce 100-m-resolution depictions of atmospheric moisture, stability, and skin temperature. The VAS, with its IR-sounding capability, provides the vertical information to the retrieval while the MAMS, with its 100-m resolution, provides the horizontal information. The retrievals show mesoscale features, including a moist tongue intrusion and an urban heat island. Mesogamma-scale gradients are found to exceed mesobeta-scale gradients, and significant mesogamma-scale variability is not captured in current geostationary sounding data. It is suggested that improvements to the spatial resolution of operating sounding data will yield improved information on atmospheric and surface gradients, especially at the mesogamma scale.

Time Trends of VAS Satellite-derived Soundings

Time tendencies of operationally prepared Visible-Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (VAS) retrievals and derived products are evaluated by comparing them against corresponding tendencies from radiosonde soundings. Temperature and dewpoint trends from the two sources are compared, as are trends of thickness and precipitable water. VAS retrieval tendencies also are compared with those of the first-guess limited-area fine-mesh model (LFM) input to determine relationships and/or improvements. Time intervals of 6 h receive the greatest attention; however, 3- and 9-h periods also are considered. Agreements between VAS and radiosonde observation (RAOB) trends generally are found to be very poor, with correlations between two versions usually less than .5. VAS trends compare less favorably with the 'ground truth' than do trends of LFM data, which served as first guess. VAS-RAOB trends of vertically integrated parameters, that is, thickness and precipitable water, agree somewhat better than those of temperature and dewpoint, but correlations still are very poor. In evaluating 3-, 6-, and 9-h intervals, statistical agreements between VAS and radiosonde trends are found to improve considerably with increasing time intervals. VAS trends are found to degrade the first-guess (LFM) trend about as often as they improve it.

A Study of Satellite-derived Moisture with Emphasis on the Gulf of Mexico

Visible-Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (VAS) moisture retrievals are compared to the National Meteorological Center Regional Analysis and Forecast System (RAFS) 12-h forecast and to 1200 UTC rawinsondes over the U.S. and the Gulf of Mexico on a daily basis for nearly 1.5 years. The principal objective is to determine what information the current moisture retrievals add to that available from the RAFS and surface data. The data are examined from the climatological perspective, that is, total precipitable water over the seasons for three geographical regions, and also for synoptic applications, that is, vertical and horizontal resolution. VAS retrievals are found to be systematically too moist at higher values. The variance of the VAS soundings more closely agrees with the rawinsonde at locations around the Gulf of Mexico than the RAFS. An examination of a case (6 June 1989) over the Gulf of Mexico region comparing three layers of VAS-derived moisture to the RAFS forecast shows the former capable of outperforming the latter in both the horizontal and, to some extent, the vertical frame of reference.

NOAA satellite observing systems: status and plans

NOAA's National Environmental Satellite, Data, and Information Service (NESDIS) operates separates series of environmental monitoring satellites in polar and geostationary orbits. Two geostationary spacecraft are normally in opration: one stationed at 75° E longitude (GOES-EAST), and one stationed at 135° W longitude (GOES-WEST). Owing to a combination of premature in-orbit failures and a launch failure there is only one GOES satellite currently operational, GOES-7, which is migrated between 95° and 105° W longitude depending upon season. GOES-7 was launched in February 1987. Its primary observing instrument is a combined imager/sounder, the VISSR Atmospheric Sounder (VAS). The first in the next series of GOES satellite, (GOES I-M), is scheduled for launch in 1992. The major upgrade over the current GOES satellites will be the introduction of simultaneous imaging and sounding capability and improvements in imaging IR and sounding resolution. Because of the long lead times necessary in designing and building new systems, NOAA, in cooperation with NASA, has already begun the planning and study process for the GOES-N series of satellites, which will fly early in the next century. NOAA operates a two polar satellite system with equatorial nodal crossing times of 0730 (descending) and 1345 (ascending). The current operational satellites are NOAA-10 (AM) and NOAA-11 (PM). The next in the series (NOAA-D, which will become NOAA-12 once operational) is scheduled for launch in early summer 1991. The instruments onboard are used to make global measurements of numerous parameters such as atmospheric temperature, water vapor, ozone, sea surface temperature, sea ice, and vegetation. The NOAA K-N series of satellites, scheduled for deployment in the mid 1990's, will provide upgraded imaging and sounding capability. The imager will be enhanced to include a sixth channel for cloud/ice descrimination. A 15 channel advanced microwave sounder will be manifested for atmospheric temperature retrievals, and a seperate 5 channel advanced microwave sounder will be used for atmospheric water vapor retrievals. The polar program will undergo major changes beginning in the late 1990's. The morning polar metsat service will become the responsibility of the Europeans with NOAA providing an operational sensor payload. The afternoon metsat service will be continued by NOAA with a new block of satellites and instruments beginning at NOAA-O. NOAA will also be closely cooperating with NASA in this time frame. A number of the instruments on NASA's Earth Observing System (EOS) platforms, scheduled for launch beginning in the late 1990's, have been designated “prototype operational” and may become candidates for eventual flight on NOAA operational spacecraft.

Monitoring Precipitable Water and Surface Wind over the Gulf of Mexico from Microwave and VAS Satellite Imagery

Abstract Spatial and temporal changes of atmospheric water vapor and surface wind speeds are investigated for a period following an intrusion of cold continental air over the Gulf of Mexico, during the Gulf of Mexico Experiment (GUFMEX) in March 1988. Microwave and infrared satellite measurements from the Special Sensor Microwave/Imager (SSM/I) instrument aboard the Defense Meteorological Satellite Project (DMSP) F8 satellite and from the GOES VISSR Atmospheric Sounder (VAS) are used to augment the sparse coverage of rawinsonde sites and surface reports in the vicinity of the Gulf of Mexico. Total precipitable water is derived from both instruments and from rawinsonde measurements at coastal locations and auxiliary sites on ships and platforms over the Gulf. Accuracies of the precipitable water derived from SSM/I and GOES are comparable, though microwave data provide more uniform coverage, when they are available, than VAS since they are relatively free from contamination by most clouds. Also, the moistur...

Analysis of Sudden Mesoscale Drying at the Surface

Mesoscale surface data and special satellite-derived soundings from the Visible Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (VAS) are used to investigate a case of sudden mesoscale drying at the surface on 17 June 1986, a day during the Cooperative Huntsville Meteorological Experiment (COHMEX). Dewpoints fall as much as −6.3°C in less than 1 h over a small portion of central Tennessee. The drying occurs prior to the onset of convective activity. The satellite retrievals detect a narrow tongue of midtropospheric dry air that overlays moist air near the surface. The analyses indicate that heating-induced surface-based mixing penetrates the midlevels, bringing drier air to the surface and resulting in the sudden decreases in surface dewpoints.

Some Comparisons of VAS and Dropwindsonde Data over the Subtropical Atlantic

Abstract Omega dropwindsonde and other in situ (INS) data collected during the NOAA/Hurricane Research Division's (HRD) Hurricane Field Program are used as a ground truth dataset for the evaluation of VISSR Atmospheric Sounder (VAS) soundings over the subtropical Atlantic. The experiments were coordinated with the Cooperative Institute for Meteorological Satellite Services at the University of Wisconsin. The focus of this study is to determine whether soundings derived from VAS radiances are an improvement over the first-guess data used as a starting point in the sounding retrieval process. First guess inputs for this study are provided by NMCs Regional Analysis and Forecast System (RAFS) nested grid model (NGM). In a case study, an objective algorithm is used to analyze the INS, VAS, and first-guess data at and below 500 mb from an HRD experiment on 1–2 September 1988. The case study is supplemented by a statistical investigation of data composited from other HRD experiments. In particular, we examine VA...

Retrieval of Precipitable Water from Observations in the Split Window over Varying Surface Temperatures

Abstract The split window technique makes use of two differentially absorbing channels in the 11 μm region to remove the attenuating effects of atmospheric absorption so as to achieve a better estimate of the underlying skin temperature than could be produced by a single channel measurement. Since the primary absorber in this region is water vapor, it follows that split window measurements should be able to produce bulk water vapor retrievals as well. When observations are made with split window channels under conditions where the surface contribution to measured radiance changes, but the atmospheric contribution does not, it is possible to estimate the ratio of the transmittance of the two split window channels. This transmittance ratio is inversely related to precipitable water. This paper applies this technique to observations from the Advanced Very High Resolution Radiometer, and the VISSR Atmospheric Sounder, and demonstrates the capability of both instruments to determine precipitable water under tw...

Mesoscale Analysis by Numerical Modeling Coupled with Sounding Retrieval from Satellites

Abstract The development and evaluation of a system for time-continuous mesoscale analysis is presented, with a focus on retrieving water vapor concentrations and ground surface temperatures from VISSR Atmospheric Sounder (VAS) data. The analysis system is distinguished by an intimate coupling of retrieval and numerical modeling processes that avoids some of the problem researchers have encountered when satellite-retrieved parameters have been input to models. The system incorporates virtually all of the temporal, vertical and horizontal structure that can be resolved in VAS soundings while maintaining model-generated gradients. The two primary components of the system are a version of the CSU Regional Atmospheric Modeling System (RAMS) and an algorithm for retrieving meteorological parameters from VAS data. The analysis system was evaluated by means of simulations, with a domain that consisted of a vertical cross section through a broad mountain slope. The purposes were to determine the accuracy of coupl...

Preconvective Mesoscale Analysis over Irregular Terrain with a Satellite-Model Coupled System

Abstract Influences on the mesoscale distribution of summertime convective cloud development in the northeastern Colorado region are described using a new system for time-continuous mesoscale analysis. The analysis system is distinctive in that there is an intimate coupling between integration of a numerical model and retrieval of temperature and water vapor concentrations from VISSR Atmospheric Sounder (VAS) data. We present a case study to compare results of the coupled analysis method with those of related methods, focusing on the roles of variations in ground surface temperatures and water vapor concentrations. The horizontal and time variations represented in satellite-based (coupled) surface temperature analyses closely corresponded to information from conventional shelter temperature observations, but had much greater detail. In contrast, temperature based on energy balance computations tended to increase too quickly during the morning and were lacking in mesoscale feature. In the water vapor analy...

Environmental Conditions Associated with the Dallas Microburst Storm Determined from Satellite Soundings

Abstract The thermodynamic structure of the troposphere in the vicinity of the microburst storm at Dallas-Ft. Worth Airport (DFW), Texas on 2 August 1985 is described. The analysis was based principally on a set of vertical soundings from the Visible and Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (VAS) onboard the Geostationary Operational Environmental Satellite (GOES), valid about 1 h before the occurrence of peak surface winds. Convection in the DFW area developed in a gradient of stability on the west side of a tongue of low lifted index and high precipitable water. The lapse rates in the 850 mb-700 mb layer were large (8°–9°C km−1). Vertical profiles of VAS data showed that DFW was in a transition zone in which conditions became drier at all levels and slightly warmer near 500 mb to the south and southwest. The midlevel warming reduced the buoyant energy available above cloud base, thus acting as a capping mechanism for the unstable, northward- moving low-level air. The potential insta...

VAS Retrievals as a Source of Information for Convective Weather Forecasts: An Objective Assessment and Comparison with Other Sources of Upper-Air Observations

Abstract Objective experiments have been carried out to determine which moisture and stability indices as derived from the VISSR Atmospheric Sounder (VAS) contain the greatest amount of predictive information with respect to thunderstorm and severe local storm events. In these experiments, stability and moisture parameters derived from 1700 UTC VAS retrievals were compared and correlated to storm observations made during the subsequent 2000–0000 UTC period. The amount of predictive information in these indices was also compared to that possessed by indices derived from VAS first-guess profiles, concurrently available rawinsonde measurements, and numerical model forecasts. The correlation in the form of the computed information ratio (Ic) was used as a measure of predictive power in these experiments. It was found that precipitable water and modified versions of the classic K index which included recent surface data had the highest values of Ic for general thunderstorm occurrence. The 50-kPa gradient wind ...

Structure and Dynamics of the Arizona Monsoon Boundary

The Arizona Monsoon Boundary is defined as the boundary separating two distinctly different air masses over Mexico and the adjacent Pacific during the summer. The structure and dynamics of this boundary are examined by cross-sectional analysis using three different data sources: 1) a composite cross section through the boundary, constructed from the Fleet Numerical Oceanography Center (FNOC) analysis; 2) a time-height cross section, constructed using radiosonde observations at the time the boundary passed through Tucson in 1984; and 3) a cross section through the boundary on 22 July 1985, using high-resolution fields of temperature, moisture, and geopotential height obtained from the VISSR Atmospheric Sounder (VAS). All draw cross sections showed similar structure. In some respects, the Arizona monsoon boundary resembles a midlatitude front (i.e., there is a distinct and relatively sharp air mass change) forced almost entirely by confluence. A direct ageostrophic circulation is produced by this forcing, giving weak ascent on the warm, moist side of the boundary. The gradients and flow associated with the composite boundary are weaker, by a factor of four, than those associated with strong midlatitude fronts. However, the VAS cross section suggests that, at times, the strength of the boundary approaches that of midlatitude fronts. The wind shear suggested by the composite boundary ought to be unstable to baroclinic or barotropic processes and, hence, disturbances developing along the boundary are a distinct possibility. These disturbances are indeed observed and are the subject of a companion paper by Moore et al.

A Method for Combining Radiances and Wind Shear to Define the Temperature Structure of the Atmosphere

Abstract The retrieval of temperature from satellite-observed radiances has traditionally been addressed as a one-dimensional or columnar problem which uses a guess profile of temperature. In this study, the traditional approach is augmented by incorporating observed wind shear as a general thermal wind constraint in the inversion of radiances to make a three-dimensional temperature analysis. The problem is cast as a classical variational problem that minimizes a weighted sum of squares subject to constraint. The constraints are the general thermal wind equation and a set of regression equations expressing the radiances in terms of the temperature profile. The solution is found by the method of conjugate gradients. Experiments using observed winds with both simulated and observed radiances for the GOES VISSR Atmospheric Sounder (VAS) are described. In both cases, a first guess from a numerical forecast is used. Simulated radiances are used to establish the optimal relative weighting of the wind versus rad...

Atmospheric Absorption in the VAS Split-Window Channels

Abstract The Visible Infrared Spin-Scan Radiometer (VISSR) Atmospheric Sounder (VAS) split-window channels at 10–12.5 μm and 12.6–12.8 μm can be used to give measurements of sea surface temperature (SST) and precipitable water amount in the lower troposphere. Empirical algorithms for providing these quantities have been developed by comparing conventional ground based measurements with the satellite data. Chesters et al. (1987) produced new differential absorption coefficients for the VAS split-window channels which, when used in a transmission model of the atmosphere, reproduce their optimized precipitable water algorithm. These new coefficients are used here in a spectral band model to see if they also improve the match between empirical and theoretical (model derived) SST algorithms. Some improvement is found but the analysis suggests that the absorption coefficient of a dry atmosphere in the 12.7 μm channel should be less than that for the 10–12.5 μm channel. In contrast, the differential absorption c...

A Spectral Approach to the Unification of Satellite and Conventional Temperature Data

A method for combining temperature soundings derived from VISSR Atmospheric Sounder (VAS) radiance observations with conventional data is presented. Using data from the Atmospheric Variability Experiment/VAS Ground Truth Field Experiment, temperature profiles from rawinsonde and VAS observations were represented by Fourier cosine series, with harmonic-by-harmonic comparisons performed for collocated pairs as well as the spatial variations of harmonic coefficients. The zeroth and first harmonics in the VAS temperature soundings were combined with higher harmonics determined from conventional data to form a unified dataset. The quality of the unified data was examined by comparing the vertical motion fields derived from a linear balance model with satellite observations of cloud systems. Case studies at 1200 UTC on August 22, 23, and 24, 1983 over the western Atlantic gave good results.