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V. V. Salomonson

Abstract

Comparisons are made between winds obtained from EOLE balloons and winds determined from cloud motions as observed from the Applications Technology Satellites, ATS-1 and ATS-3. The results show that the mean winds determined from EOLE balloons are greater in speed than mean winds derived from cloud motion observations. Inspection of the total set of comparisons lead one to conclude that the cloud motion winds in the 20–50°S latitude band apply to a level lower than 200 mb. The mean differences become smaller toward the equator and the results further suggest that the cloud motion winds apply to altitudes higher than 200 mb equatorward of 20°S.

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V. V. Salomonson and W. E. Marlatt

Abstract

Integrated directional reflectances and relative anisotropy were measured over stratus clouds, snow and white gypsum sand using the Nimbus F-3 medium resolution radiometer (MRIR) and a siliconcell pyranometer mounted on a Piper Twin Comanche. Reflectances in the 0.2–4.0 and 0.55–0.85 μ portions of the solar spectrum were investigated. Eight flights were completed in different geographic areas over stratus clouds of varying thicknesses. Three flights were made over snow in two different localities and five flights were made over white sand found in the White Sands National Monument, N. Mex.

The greatest anisotropy in scattered radiation was observed over stratus clouds. This anisotropy was composed of strong forward scattering and less pronounced backscattering. The anisotropy observed in the radiation reflected from snow was primarily due to specular reflection in the forward direction. Reflection back toward the sun was the predominant feature in the reflectance distributions observed over gypsum sand. The results demonstrate the interaction of the spectral reflectivity of the surface, the spectral response of the instrument, and the spectral character of the energy impinging upon the reflecting surface.

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William E. Shenk and Vincent V. Salomonson

Abstract

The effect of sensor spatial resolution on estimating the amount of clouds covering the earth were investigated by simulating various cloud distributions and sizes, and measuring the known cloud amount with resolution of different sizes cloud-no cloud threshold technique often applied in automatic data processing. Cloud amount statistics have been tabulated for a three-orders-of-magnitude range in the ratio (R) of areal cloud size to areal resolution size for seven cloud amounts between 6 and 90%. Three different cloud patterns were used. These were 1) a regularly spaced pattern of homogeneous dots arranged in rows and columns (to simulate cloud streets), 2) a randomly spaced pattern of the same dots (to simulate randomly oriented cumulus clouds), and 3) a heterogeneous cloud size distribution irregularly spaced (to simulate a view of different cloud types and sizes). Two cloud amount estimation techniques were tested. Cloud amounts of 100% (method 1) and 50% (method 2) were assigned to partially filled resolution elements. Using criteria applicable to some studies carried out in the past, it is shown that cloud amount estimations can be in error by as much as 86% and 38%, respectively, for the two methods. Nomograms have been developed which substantially improve the estimate of the true cloud cover for R < 100 provided that R can be determined. Good agreement was found when a check was performed on whether or not the simulated cloud patterns were representative of real cloud patterns. The check was made by testing the cloud cover estimate nomograms constructed with the simulated data against similar curves prepared from cloud fields extracted from high-resolution photographs obtained from an Apollo flight.

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FRANK L. MARTIN and VINCENT V. SALOMONSON

Abstract

Stepwise linear regressions for the specification of blackbody surface radiances are computed using a set of 103 model atmospheres chosen originally by Wark et al. and the corresponding simulated values of Nimbus 2 window-channel (10–11 µ) radiances. Two stratifications are considered: (a) precipitable water vapor, u>1, and (b) u<1 gm cm–2. For each of five zenith angles considered, significant contributions are made in both regression formulas by inclusion of parameters representing the radiative transfer effects of water vapor and ozone. This regression formulation makes use of empirically derived expressions related to these effects over long atmospheric paths. The specification of the sample of surface radiances is in accordance with a multiple correlation coefficient, exceeding 0.990 and 0.995 in the respective stratifications. Corrections for atmospheric effects to be applied to Nimbus 2 window-channel radiances in estimating the corresponding surface values are displayed in nomogramic as well as analytic forms.

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William E. Shenk and Vincent V. Salomonson

Abstract

Three channels of the Nimbus 2 five-channel Medium Resolution Infrared Radiometer (MRIR) have been employed in the development of a technique to determine sea surface temperature. Two of the channelsin the 0.2-4.0 and 6.4-6.9 μm spectral regions are used to indicate a cloud-free line of slight and the third, a high signal-to-noise window channel (10-11 μm), measures the equivalent blackbody temperature (TBB) which is a function of the thermal emission from the sea surface and the intervening atmosphere. Equivalent blackbody temperatures and normalized reflectance thresholds were established using frequency distributions from the 6.4-6.9 and 0.2-4.0 μm channels, respectively, to determine the existence of cloud-free conditions. The window TBB's were compared with ship ocean temperature measurements for a one-month period over the western North Atlantic. This comparison revealed a ±1.5K dispersion about the mean difference between the ship temperatures and window TBB's between 31-34N. An empirical method has been developed to correct for the atmospheric contribution to the observed window TBB's that considers the measurements from the other two channels and the viewing angle from the radiometer to the ocean surface.

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Joseph Steranka, Lewis J. Allison, and Vincent V. Salomonson

Abstract

The Nimbus 4 Temperature-Humidity Infrared Radiometer (THIR) monitors radiation in the 6.5–7.2 μm water vapor absorption region with a 23-km spatial resolution at the sub-satelite point. Radiation monitored in this spectral region results primarily from emission in the 250–500 mb region of the upper troposphere. The THIR 6.7μm observations are readily available in photofacsimile imagery form which shows very distinctive patterns associated with spatial variations in atmospheric water vapor.

These radiometric observations have been combined in several instances with moisture values measured in the upper troposphere by the standard radiosonde network. In each instance, the result is a much more consistent analysis showing increased spatial detail that agrees with the radiometric observations and does not compromise the conventional data. The improved moisture analyses show relatively dry and moist tongues that are very difficult or impossible to infer from the conventional data alone. The patterns in the moisture fields can be tracked over 12- and 24-hr periods. In addition, by keeping in mind the advective properties of the moisture field, success has been achieved in improving streamline analyses at the 400-mb level over data-sparse regions on a global scale.

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William E. Shenk, Herbert E. Hunter, Frederick V. Menkello, Robert Holub, and Vincent V. Salomonson

Abstract

An objective statistical procedure has been developed using satellite infrared window radiation measurements to estimate the central pressure (Pc), the deviation of the central pressure from the climatological normal (ΔP), the intensity (I = ∇2 P), and the deepening or filling rate (dP/dt) of extratropical cyclones. The independent variables for 40 cylones over the North Atlantic and Pacific Oceans were the Nimbus 2 High Resolution Infrared Radiometer (HRIR) measurements at 79 locations surrounding the center of each cyclone, the date, and the geographical location of the center. Optimum empirical orthogonal functions were used to reduce the dimensionality and establish the regression relationship between the cyclone parameters and the radiation measurements for 30 of the cyclones. The remaining 10 cyclones were used to test the accuracy of the regression relationship. When the test cyclones were well represented by the cyclones in the sample employed to establish the relationship, a standard error of estimate for Pc of 6 mb was achieved for the test cyclones with slightly lower percentage accuracies for ΔP and I. An a priori decision could be made for each test cyclone regarding the probable success of parameter estimation. This was dependent on how well the test cyclone was represented by the orthogonal functions derived by the cyclones used to establish the regression equation.

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C. Prabhakara, V. V. Salomonson, B. J. Conrath, J. Sterania, and L. J. Allison

Abstract

Remote soundings of total ozone made by the Infrared Interferometer Spectrometer onboard the Nimbus 3 satellite, during June and July 1969, show the presence of ozone minima over northeast India and north Africa where summertime upper air high pressure systems exist. The easterly jet stream is revealed by ozone maxima observed along its path over southeast Asia and Africa during the summer monsoon period.

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William E. Shenk, Hugh Powell, Vincent V. Salomonson, and William R. Bandeen

Abstract

The stereographic horizon map projection is a generalized form of the polar stereographic projection that permits placement of the map center at any point on the earth. With this projection, it is possible to view translating meteorological systems in one perspective regardless of system location. An algorithm was developed for converting a polar stereographic projection to a stereographic horizon projection. Two types of meteorological systems were examined with meteorological satellite infrared radiation data placed in the new map projection to illustrate its use. The cloud pattern evolution (as seen through an infrared atmospheric window) associated with a rapidly developing extratropical storm was used to depict how the stereo-graphic horizon map projection quantitatively reveals the major centers of cloud development, movement and dissipation relative to the cyclone center. With the stereographic horizon projection, the classical dynamic features of the ject stream appeared to be present in the appropriate quadrants of a composite of composite of Nimbus 3 infrared (6.4–6.9 μm) radiation data surrounding 13 jet stream speed maxima.

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