Spin Scan Radiometer Atmospheric Sounder Research Articles

An Evaluation ofGOES-8Retrievals

The Geostationary Operational Environmental Satellite (GOES-8) temperature–moisture retrievals were compared with collocated National Weather Service radiosonde observations (RAOBs) to assess retrieval performance. Retrieved values of temperature and dewpoint were evaluated at individual levels. Precipitable water and thickness also were evaluated, and the GOES-8 retrievals were compared with the first-guess data used in the algorithm. The dataset consisted of 1113 RAOB–retrieval pairs (collocated to within 50 km) over the United States at 1200 UTC during August–November 1995. GOES-8 temperature retrievals were found to agree better with their RAOB-derived counterparts than did the dewpoints. However, both temperatures and dewpoints were found to be highly dependent on their first-guess data from the Nested Grid Model. Retrievals generally were closer to the RAOBs than was the first guess. However, this was never guaranteed, even for large first-guess discrepancies. In fact, some retrievals did not agree as well with the RAOBs as did the first guess. GOES-8 and RAOB-derived precipitable water (PW) and thickness showed closer agreement than the level-specific data. Both integrated parameters were dependent on their first guess. However, GOES-8 and RAOB PW agreed more often in layers above the surface where the guess was less accurate. Comparison with a previous evaluation of retrievals from the Visible and Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) indicated that GOES-8 retrievals agreed better with RAOBs than did the VAS versions. This improvement is likely due to GOES-8’s increased number of channels and better signal-to-noise values, along with the assumed increase in quality of the first-guess data being used.

A Comparison of Saturation Pressure Differences and GOES VAS Estimates to Surface Observations of Cloudiness

Saturation pressure differences are calculated from upper-air soundings and compared to manual surface observations of cloudiness. The mean saturation pressure difference between 1000 and 700, 700 and 400, and 400 and 300 mb is calculated and compared to the observed composite cloudiness for those layers. Results indicate that as the absolute value of saturation pressure difference decreases toward zero, the resulting ground observed composite cloud amount increases. However, the mean saturation pressure difference for high clouds ranges from 64 mb under clear skies to 16 mb for overcast conditions. This corresponds to relative humidities between 25% and 76%. Most previous studies do not indicate such large cloud amounts at these humidities. Three empirical relationships that define low, middle, and high clouds are developed based on one year of comparisons. These relationships are then tested on an independent dataset that include a wide variety of cloud cover conditions. Qualitative comparisons are made to manual observations of cloudiness and indicate that the relationships overall slightly overestimate the frequency of cloudiness. Cloudiness derived from the Visible-Infrared Spin Scan Radiometer Atmospheric Sounder onboard the Geostationary Environmental Operational Satellite 7 using the CO{sub 2} slicing technique is also compared to surface observations. Results indicate thatmore » the satellite-derived cloudiness overestimates cloudiness compared with surface observations but is also very similar to the saturation pressure difference estimates. 12 refs., 13 figs., 3 tabs.« less

Clustering of Satellite Sounding Radiances to Investigate Intense Low-Level Humidity Gradients

Abstract Satellite-derived profiles of temperature and dewpoint (retrievals) are obtained using radiance data from the Visible-infrared Spin Scan Radiometer Atmospheric Sounder. Individual fields of view that are input to the retrieval algorithm must be horizontally averaged to provide suitable signal-to-noise ratios. This paper investigates three methods for performing this averaging: 1)a blocking approach that is employed operationally, 2) a manual procedure that seeks to maximize atmospheric gradients, and 3) an objective procedure called clustering that takes advantage of similarities in satellite measurements to avoid smearing the gradient information. The three techniques are examined on 10–11 July 1989 when intense gradients of humidity were present over the Florida peninsula. Results show that the clustering scheme produced retrievals that were very similar to those obtained manually. Both schemes indicated strong humidity gradients in the lower troposphere. The blocking procedure produced less intense gradients. The retrieval information is used to examine conditions leading to fair weather on 10 July but intense thunderstorm development on 11 July.

The Retrieval of Marine Stratiform Cloud Properties from Multiple Observations in the 3.9-µm Window under Conditions of Varying Solar Illumination

Abstract Radiometric observations in the 3.9-µm region have been used by a number of investigators for the determination of cloud parameters or sea surface temperature at night. Only a few attempts have been made to perform quantitative assessments of cloud and surface properties during the daytime because of the inability to distinguish between the thermal and solar components of the satellite-sensed radiances. This paper presents a new method of separating the thermal and solar components of upwelling 3.9-µm radiances. Two collocated satellite observations are made under conditions where the solar illumination angle changes but the thermal structure of the cloud and atmosphere, as well as the cloud microphysics change very little. These conditions can easily be met by observing the same cloud from geosynchoronous orbit over a short time interval during the morning hours. When the radiances are differenced under these constraints, the thermal components cancel, and the difference in the radiances is simply the difference in the solar component. With a few simplifying assumptions, a cloud microphysical property, specifically effective radius, can be inferred. This parameter is of particular importance to both climate modeling and global change studies. The methodology developed in this paper is applied to data from the Visible-Infrared Spin Scan Radiometer Atmospheric Sounder onboard the GOES-7 spacecraft for a period in August 1992.

Simulation study of the remote sensing of optical and microphysical properties of cirrus clouds from satellite IR measurements

Improved ray-optics theory and Mie theory for single scattering and an adding-doubling method for multiple scattering have been used to study the interaction of radiation in NASA's Visible and Infrared Spin-Scan Radiometer Atmospheric Sounder Satellite (VAS) IR channels and the microphysics of inhomogeneous cirrus clouds. The simulation study shows that crystal shape has remarkable effects on scattering and on the radiative-transfer properties of cirrus clouds in IR spectra. The sensitivity of the brightness temperature, as observed with VAS-IR channels, to the hexagonal columns and plates in cirrus clouds is noticeable. A method that permits one to infer the optical thickness, crystal shape, ice-water content,and emittance of cirrus clouds by using a multi-IR window channel with a scanning observation technique is developed. Detailed error analyses are carried out, and the characteristics of VAS-IR window channels are investigated through the examination of the effects of sea-surface reflection and variations in the temperature and water-vapor profiles on the VAS measurements. It is shown that these effects are large and need to be considered. Some uncertainties that have risen from the theoretical model are studied; they demonstrate that the Mie-scattering theory should not be used to retrieve the microphysical and optical properties of cirrus clouds. A suitable cloud-microphysics model and a suitable scattering model are needed instead.

Trends in South American biomass burning detected with the GOES visible infrared spin scan radiometer atmospheric sounder from 1983 to 1991

In an effort to get a better understanding of the extent and patterns of burning in South America, geostationary satellite data have been used to monitor active fires. Previous work demonstrated the ability to manually detect subpixel fire activity in selected areas of the selva and cerrado regions in South America with shortwave and longwave infrared data available from the Geostationary Operational Environmental Satellite (GOES) visible infrared spin scan radiometer atmospheric sounder (VAS) This paper presents the GOES VAS automated biomass‐burning algorithm (ABBA) which was developed to determine basin‐wide trends in fire activity in South America utilizing the GOES VAS archive. Comparisons between the manual and the automated techniques revealed that overall, the ABBA proved to be more consistent in identifying fires and better suited for trend analysis. The automated algorithm was applied daily to a study area extending from 5°S to 15°S and from 45°W to 70°W for 2 weeks at the peak of the burning seasons in South America in 1983, 1988, 1989, and 1991 in an effort to measure the areal extent of burning in South America during the past decade and to provide additional insight into the diurnal signature in satellite detection of biomass‐burning activities. The expansion of the regions of burning are readily detected in a comparison of these 4 years. From 1983 to 1991 the amount of burning detected by the GOES VAS ABBA during these 2‐week periods nearly doubled in the selva and mixed regions and tripled in the cerrado. Diurnal analyses confirmed earlier results indicating that the optimum time to monitor biomass burning is around 1530 UTC.

A Comparison of Ground and Satellite Observations of Cloud Cover

Abstract A processing scheme that determines cloud height and amount based on radiances from the Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) using a CO2 absorption technique has been installed on the National Environmental Satellite Data and Information Service VAS Data Utilization Center computer system in Washington, D.C. The processed data will complement the Automated Surface Observing System (ASOS). ASOS uses automated ground equipment that provides near-continuous observations of surface weather data that are currently manually obtained. Geostationary multispectral infrared measurements are available every hour with information on clouds above the ASOS laser ceilometer viewing limit of 12 000 ft. The combined ASOS/satellite system will be able to depict cloud conditions at all levels up to 50 000 ft. The error rate of combined ASOS and satellite observations is less than 4% of the total sample in a comparison test with manual observations performed by National Weather Service per...

Comparison of Column Water Vapor Measurements Using Downward-looking Near-Infrared and Infrared Imaging Systems and Upward-looking Microwave Radiometers

Remote soundings of precipitable water vapor from three systems are compared with each other and with ground truth from radiosondes. Ancillary data from a mesoscale network of surface observing stations and from wind-profiling radars are also used in the analysis. The three remote-sounding techniques are: (a) a reflectance technique using spectral data collected by the Airborne Visible-Infrared Imaging Spectrometer; (b) an emission technique using Visible-Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) data acquired from the NOAA's GOES; and (c) a microwave technique using data from a limited network of three ground-based dual-channel microwave radiometers. The data were taken over the Front Range of eastern Colorado on 22-23 March 1990. The generally small differences between the three types of remote-sounding measurements are consistent with the horizontal and temporal resolutions of the instruments. The microwave and optical reflectance measurements agreed to within 0.1 cm; comparisons of the microwave data with radiosondes were also either as good or explainable. The largest differences between the VAS and the microwave radiometer at Elbert were between 0.4 and 0.5 cm and appear to be due to variable terrain within the satellite footprint.

Geostationary satellite detection of bio mass burning in South America

Abstract This paper presents the results of using Geostationary Operational Environmental Satellite (GOES) Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) data to monitor biomass burning associated with deforestation and grassland management in South America. The technique of Matson and Dozier has been adapted to GOES VAS short-wave and long-wave infrared window data to determine ihe size and temperature of fires associated with these activities. Although VAS data do not offer the spatial resolution available with Advanced Very High Resolution Radiometer (AVHRR) data (7 km versus I km) this decreased resolution does not seem to hinder the ability of the VAS instrument to delect fires; in some cases it proves to be advantageous, in that saturation does not occur as often. Sequences of VAS visible data are helpful in verifying that the hot spots sensed in the infrared are actually related to fires. Furthermore, the smoke of the fires can be tracked in time to determine their motion and traje...

Cloud characteristics over central Amazonia during GTE/ABLE 2B derived from multispectral visible and infrared spin scan radiometer atmospheric sounder observations

Multispectral GOES/Visible and Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) observations in the carbon dioxide absorption band at 15 μm have been used to calculate diurnal cloud statistics over central Amazonia region for 4 days during the Global Tropospheric Experiment/Amazon Boundary Layer Experiment (GTE/ABLE IIB). The CO2 technique calculates both cloud top pressure and effective emissivity from radiative transfer principles. Transmissive clouds that are partially transparent to terrestrial radiation have been reliably separated from opaque clouds in the statistics of cloud cover. A high incidence of transmissive clouds (about 47%) was found on the average. Diurnal characteristics of cloud cover over Amazonia have been linked to convective activity over this region. On days with afternoon convection, an increase in low‐altitude opaque clouds was followed by a subsequent increase in high‐altitude transmissive clouds.

A Simulation and Diagnostic Study of Water Vapor Image Dry Bands

A Limited Area Mesoscale Prediction System (LAMPS) model simulation and special 3-hour radiosonde dataset are used to investigate warm (dry) bands in 6,7 μm water vapor satellite imagery on 6–7 March 1982. The purpose is to reveal processes resulting in the formation and evolution of the dry features that appear as curving dark streaks in the imagery. Model soundings are input to a radiative transfer algorithm to generate synthetic 6.7 μm equivalent blackbody temperatures (TB) which are compared with those from the Visible infrared Spin Scan Radiometer Atmospheric Sounder aboard the Geostationary Operational Environmental Satellite. Simulated and radiosonde-derived vertical velocity and humidity also are compared with the images. Finally, trajectories are calculated from both radiosonde data and LAMPS output. The model reproduces major characteristics of the observed TB field. A “development” dry image feature occurs in conjunction with an upper level shortwave trough, and an “advective” feature is associated with a polar jet streak. Both model and observed TB features are associated with vorticity maxima. The development feature forms as moisture gradients are enhanced by differential subsidence early in the study period. Horizontal wind shear then narrows the incipient dry area into its streak-like shape. Trajectories reveal that air parcels ending in the development streak move with it, in northwesterly, subsiding flow throughout the study period. Near the leading edge of the streak, ahead of the short-wave trough, flow is southwesterly and ascending. Air parcels in the advective image feature sink in the wake of the vorticity maximum, move through it in the jet flow, and finally ascend ahead of it. Thus, warm TB regions do not equate with instantaneous subsidence patterns, but reflect a long history of parcel motions which can include ascent as well.

Verification of Mesoscale Objective Analyses of VAS and Rawinsonde Data Using the March 1982 AVE/VAS Special Network Data

Various combinations of VAS (Visible and Infrared Spin Scan Radiometer Atmospheric Sounder) data, conventional rawinsonde data, and gridded data from the National Weather Service's (NWS) global analysis, were used in successive-correction and variational objective-analysis procedures. Analyses are produced for 0000 GMT 7 March 1982, when the VAS sounding distribution was not greatly limited by the existence of cloud cover. The successive-correction (SC) procedure was used with VAS data alone, rawinsonde data alone, and both VAS and rawinsonde data. Variational techniques were applied in three ways. Each of these techniques was discussed.

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.

Atmospheric soundings from a geostationary satellite

A case is presented to demonstrate the accuracy of the soundings from a geostationary platform with the visible infrared spin–scan radiometer atmospheric sounder (VAS) on GOES-5. VAS radiances for this case are consistent with TOVS high resolution infrared radiation sounder radiances. VAS temperature profile retrievals agree well with those observed by radiosonde. Initializing the retrieval process with ground-based Profiler data renders an improved product. Time variations in the atmospheric state are readily discernible from VAS soundings at ∼2-h intervals.