Spin Scan Research Articles

Passive microwave remote sensing of cloud liquid water over land regions

Techniques for cloud liquid water retrieval over land are developed using data from the Special Sensor Microwave/Imager 85.5 GHz (3.5 mm) channels. To minimize the effect of surface emittance variability on the calculations, the surface emittance was estimated with the aid of surface skin temperature retrievals from the Visible Infrared Spin Scan Radiometer in geosynchronous orbit. The high sensitivity of the 85.5 GHz channels to cloud liquid water allows for the estimation of integrated cloud liquid water based on the microwave brightness temperature depression caused by attenuation and emission of microwave radiation at the colder ambient temperature of the cloud. The method assumes nonscattering radiative processes are dominant, therefore only nonprecipitating cloud liquid water is considered. Integrated cloud liquid water retrievals show good qualitative agreement with other available data sources. Numerical error sensitivity analysis show integrated cloud liquid water error estimates of 0.05–0.50 kg m−2 depending on the contrast of cloud over background.

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.

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...

Present status and future plans of the Japanese earth observation satellite program

Japan is now operating 3 earth observation satellites, i. e. MOS-1 (Marine Observation Satellite-1, Momo-1 in Japanese), EGS (Experimental Geodetic Satellite, Ajisai in Japanese) and GMS (Geostationary Meteorological Satellite, Himawari in Japanese). MOS-1 has 3 different sensors, MESSR (Multispectral Electronic Self Scanning Radiometer), VTIR (Visible and Thermal Infrared Radiometer) and MSR (Microwave Scanning Radiometer) in addition to DCS (Data Collection System). GMS has two sensors, VISSR (Visible and IR Spin Scan Radiometer) and SEM (Solar Environmental Monitor). EGS is equipped with reflecting mirrors of the sun light and laser reflecters. For the future earth observation satellites, ERS-1 (Earth Resources Satellite-1), MOS-1b, ADEOS (Advanced Earth Observing Satellite) are under development. Two sensors, AMSR (Advanced Microwave Scanning Radiometer) and ITIR (Intermediate Thermal IR Radiometer) for NASA's polar platform are initial stage of development. Study and planning are made for future earth observation satellites including Japanese polor platform, TRMM, etc.). The study for the second generation GMS has been made by the Committee on the Function of Future GMS under the request of Japan Meteorological Agency in FY 1987.

Auroral energy deposition rate, characteristic electron energy, and ionospheric parameters derived from Dynamics Explorer 1 images

Auroral images acquired by the Spin Scan Auroral Imager (SAI) on board the DE 1 satellite are converted to geophysical parameters by applying the physical processes that produce the images from a precipitating electron flux to the response characteristics of the instrument. The energy flux and the characteristic energy are the basic derived parameters from which several ionospheric properties may be computed. Two spectral emissions are required to specify the characteristic energy and the energy flux. With the complement of available filters and photometers the combination of an ultraviolet channel and one emission in the visible wavelength region is necessary and sufficient for the purpose. The images provide global parameters at 12‐min temporal resolution; however, the spatial resolution is limited by the field of view of a pixel. Thus, images acquired from satellites at several Earth radii are useful for specifying auroral parameters to be used in time dependent global models of the ionosphere and thermosphere. In view of the variable spatial structure in the auroral oval the analysis of 12‐min images presented in this paper yields a better representation of ionospheric parameters than empirical models based on local measurements averaged over long periods of time.

Multispectral sensor data simulation modeling based on the multiple scattering LOWTRAN code

A method for simulating satellite channel radiances is described which would be useful for sensor response evaluation and channel optimization studies. Emergent radiance spectra are calculated for wavelengths between 0.4 and 13.0 μm using a modified version of the AFGL LOWTRAN transmittance/radiance code which includes the effects of multiple scattering. These radiance spectra, calculated for a sensor's specific solar illumination condition, are channel bandpass weighted to simulate sensor channel radiance sensitivities to surface—atmosphere properties. This method can produce channel radiances of most earth resources and cloud field multispectral imagers including the Landsat Thematic Mapper (TM) and Multispectral Scanner (MSS), the NOAA Advanced Very High Resolution Radiometer (AVHRR), the GOES Visible Infrared Spin Scan Radiometer (VISSR), the Defense Meteorological Satellite Program's (DMSP) Operational Linescan System (OLS), and Multispectral Operational Linescan System (MSOLS). A variety of realistic remote sensing scenarios are illustrated for selected instruments and fields-of-view containing hazes, fogs, and water and ice clouds observed against surface backgrounds including the ocean surface, land, vegetation, and snow cover. Actual Landsat TM and MSS visible and near infrared data obtained for clear and cloudy fields-of-view are compared to simulated channel radiances to assess the model's accuracy and representativeness.

A cloudy-sky radiative transfer model suitable for calibration of satellite sensors

We present a radiative transfer model suitable for calibration of satellite instruments sensing in the solar spectrum. The model consists of two clear layers sandwiching a plane-parallel cloud layer. Clear-sky optical effects are treated with modified Beer's Law relationships and cloud optical effects are treated with the delta-Eddington method. We use a model inversion process to determine an effective cloud optical depth from surface measurements of global irradiance and then use the model to calculate the corresponding upward irradiance at the top of the atmosphere. Upward irradiances are converted into directional radiances using empirical bidirectional reflectance factors. The model radiances are then compared to simultaneous satellite measurements of radiances from the cloud tops over the surface site. We compare model results to observations of the GOES Visible and Infrared Spin Scan Radiometer. Results indicate that the VISSR band (0.55–0.75 μm) radiance is close to nominal (slope 0.9601 compared to the expected 1.0). Significant, approximately cubic-form nonlinearity of response is found (consistent with the amount of nonlinearity exhibited on prelaunch calibrations). Equivalent broad-band radiance also suffers from the same type of nonlinear response, with the best linear slope being about 80% of nominal, a result consistent with that anticipated for narrow-band to broad-band conversion. Observed root-mean-square errors for sensor calibration results are comparable to those found in direct comparison between uncalibrated and calibrated sensors on different satellites, indicating that the cloud-calibration approach has merit as a means of quantitative satellite sensor calibration.

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.

Downward longwave irradiance at the ocean surface from satellite data: Methodology and in situ validation

A methodology is presented for estimating downward longwave irradiance at the ocean surface from satellite radiance data. The downward longwave irradiance is computed with a fast and accurate radiative transfer model as a function of temperature, water vapor, ozone and carbon dioxide mixing ratios, fractional cloud coverage, emissivity of clouds, and cloud top and cloud base altitudes. A sensitivity study is performed to assess the relative importance of the model input parameters and devise strategies regarding their retrieval. Ozone and carbon dioxide mixing ratios are consequently fixed at their climatological values, whereas the other parameters, highly variable in space and time, are determined from satellite data. Temperature and water vapor mixing ratio are obtained from NOAA Tiros operational vertical sounder data, and cloud parameters are retrieved from GOES visible and infrared spin scan radiometer data. Several methods are investigated to retrieve the cloud parameters. In the most refined method, cloud base altitude is deduced from cloud top altitude and liquid water path, assuming a vertical liquid water distribution within the clouds. In the other methods, simplifying assumptions are introduced, which include directly relating liquid water path to cloud geometrical thickness, fixing the cloud geometrical thickness to its climatological value, and, finally, parameterizing the cloud effects only as a function of fractional cloud coverage. Satellite‐derived irradiances are compared to those measured in situ during the Mixed Layer Dynamic Experiment, conducted in October–November 1983 off the central California coast. The results indicate that the satellite methods perform similarly, with standard errors of estimate ranging from 21 to 27 W m−2 on a half‐hourly time scale and from 16 to 22 W m−2 on a daily time scale. These errors correspond to 6 to 8% and 4 to 6% of the average measured values, respectively. When compared with techniques based on empirical formulas that employ conventional surface data, the satellite methods also exhibit similar standard errors of estimate. The satellite methods, however, are favored, since they are generally less biased and globally applicable.

Simulations of the GOES visible sensor to changing surface and atmospheric conditions

Numerical experiments have been conducted to simulate the GOES Visible and Infrared Spin Scan Radiometer (VISSR) visible sensor's response under varying surface and atmospheric conditions, as a function of solar zenith angle. The possible bias in the information obtained with this limited spectral response sensor was assessed by comparing the narrow‐band filtered clear‐sky planetary albedo, as observable with the VISSR, with the broadband (0.3–2.5 μm) unfiltered planetary albedo under the same environmental conditions. Four cases of wavelength‐dependent surface albedo (snow, meadow, dry sand, and water) and three atmospheric conditions have been simulated. It was demonstrated that the relationship between the filtered and the broadband planetary albedo depends primarily on the assumptions made about the magnitude and wavelength dependence of the surface albedo and, to a lesser extent, on the atmospheric conditions. Under certain circumstances (e.g., dry sand, water), the two were found to be in close agreement. For snow the filtered albedo exceeds the broadband albedo for all zenith angles; for meadow the broadband albedo will exceed the filtered albedo. Regression equations were derived to transform the VISSR filtered albedo to unfiltered broadband albedo for each surface type.

Satellite Observations of Hurricane Elena (1985) Using the VAS 6.7-μm “Water-Vapor” Channel

Satellite imagery from the VISSR (Visible Infrared Spin Scan Radiometer) Atmospheric Sounder (VAS) 6.7-μm water-vapor absorption band is normally available to the National Hurricane Center (NHC) in real time (half-hourly intervals, 16 hours a day) through a remote Man-computer Interactive Data Access System (McIDAS) workstation located in the forecast center. Synoptic features that are not readily apparent in “visible” imagery or “11-μm-infrared” imagery are often well defined in the VAS “water-vapor” imagery with the help of special enhancement software that exists on McIDAS. A good example is Hurricane Elena (1985). Its erratic path in the Gulf of Mexico was responsible for the evacuation of nearly a million people in low-lying coastal areas during a three-day period. Imagery from the VAS 6.7-μm water-vapor channel clearly shows the interaction of a midlatitude trough with the hurricane, and supports other evidence that suggests this was responsible for altering Elena's course.

Geocoronal imaging with Dynamics Explorer

The ultraviolet photometer of the University of Iowa spin scan auroral imaging instrumentation on board the Dynamics Explorer 1 satellite has returned numerous images of the geocorona from altitudes of 570 km to 23,300 km. The geocoronal observations from 1981 through 1985 are compared to a spherically symmetric isothermal Chamberlain model of the exospheric density distribution. Model parameters are varied to obtain an acceptable fit. The radiative transfer equation is solved numerically. Stellar intensities are monitored for an independent calibration of the DE 1 instrument in flight. The solar Ly α flux is estimated through concurrent measurements made by the Solar Mesosphere Explorer satellite, supplemented by published values of ground‐observable solar indices. Extraterrestrial background intensities are adopted from earlier OGO 5 high‐altitude measurements. The optimum fit for 1981 imaging data utilizes a Chamberlain model of temperature T = 1050 K and exobase density nc = 44,000 atoms cm−3. The exobase is taken as rc = 1.08 RE (500 km altitude), and a critical radius for satellite atoms of rcs = 3.0 rc is adopted. This model continues to compare well with the DE 1 measurements over the entire 4‐year period studied, even though the exobase conditions are expected to have changed appreciably during this interval of declining solar activity. It is concluded that the apparently constant hydrogen density and scale height observed by DE 1 are not directly indicative of the exobase conditions through the classical Chamberlain model but rather show the effects of charge exchange with thermal ions in the plasmasphere. A readily observable departure from spherical symmetry is the geotail, an enhancement in the atomic hydrogen column densities in the antisunward direction.

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.

Comparison of winter-nocturnal geostationary satellite infrared-surface temperature with shelter—height temperature in Florida

Geostationary satellite surface temperatures derived from a Visible and Infrared Spin Scan Radiometer ( vissr) sensor (10.5 to 12.6 microns) were compared with 1.5-m air temperatures collected by a thermocouple on a traversing vehicle along rural highway transects in Florida, and with two fixed thermographs located in rural and agricultural areas. Statistical comparisons between satellite and 1.5-m observations yielded a mean correlation coefficient of 0.87 and an average sample standard deviation from regression of 1.57°C during clear nights for four winters (1978–1981). The satellite-temperature image of Lake Okeechobee was compared with its geographic outline for areal image registration. Manual overlays of temporal images were repeatable to within one pixel. Satellite-sensed water temperature of Lake Okeechobee was used as an indicator of satellite radiometer repeatability and stability.

A Satellite Stereoscopic Technique to Estimate Tropical Cyclone Intensity

The techniques used to obtain the mean equivalent temperature of the eye wall for Hurricanes Frederic (1979) and Allen (1980) using GOES satellite IR and stereoscopic observations are described. The eye wall is the area of greatest convection near the center of the storm, and is bounded by the inner radius around the eye and the outer radius bounding the area of inner core convection. The stereoscopic capability afforded by the GOES West and East spacecraft permits simultaneous, two-view imagery of a tropical cyclone, yielding height measurement accuracies of 0.5 km and horizontal accuracies as small as 1 km. An airborne lidar unit was used to verify the height measurements made of Hurricane Frederic. At the same time, the GOES East Visible IR Spin Scan Radiometer (VISSR) provided the mean wall temperatures from the release of latent heat. The trials aided in identifying the assumptions and consequent inaccuracies introduced into the temperature sounding data during analysis. The satellite data is concluded useful for monitoring changes in storm intensity.

Visible infrared spin–scan radiometer atmospheric sounder radiometric calibration: an inflight evaluation from intercomparisons with HIRS and radiosonde measurements

The Visible IR spin-scan radiometer Atmospheric Sounder (VAS) is the first sounding instrument placed in geostationary orbit. The calibration procedure for determining VAS radiances requires modeling the contributions of the telescope foreoptics components to the background radiation. A simple relation between target radiance and detector output voltage is derived. The calibration procedure is successfully tested by comparisons with HIRS and radiosonde data. After removing a negative offset of up to 3 degrees C in three of the upper atmospheric CO(2) bands of VAS, the capability to produce accurate soundings (within 2 degrees C of radiosonde) was demonstrated.

Storm observation

The Goes‐D meteorological satellite (see figure) was launched September 9 from the Kennedy Space Center. It carried a new type of instrument known as the VAS, or Visible Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder. NASA's Goddard Space Flight Center, Greenbelt, Maryland, and t he University of Wisconsin at Madison will conduct a long‐term experiment to evaluate this instrument's usefulness in t he prediction of severe local hurricanes, storms, and other short‐term weather phenomena.Previous Goes spacecraft provided day and night, two‐dimensional cloud cover photos. Now, the new atmospheric sounder, in addition to this same imaging capability, will be able to measure atmospheric temperatures and moisture at various altitude layers. As with previous Goes satellites the new instrument will provide both day and night cloud cover photos with a resolution of approximately 0.9 km in daylight and 6.9 km at night.

A signal demultiplexer for Meteosat primary data user stations

Digital signals received from the Meteosat satellite consist of a serial bit stream which contains the output of the satellite's spin scan radiometer after computer processing at Darmstadt, Germany. This paper describes a system which recognizes the particular format being transmitted, picks out a chosen channel from the data, and turns it into a form suitable for display on a facsimile recorder or similar instrument.