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NASA NTRS1986

Overview of VEGA Venus balloon in situ meteorological measurements

The VEGA balloons made in situ measurements of pressure, temperature, vertical wind velocity, ambient light, frequency of lightning, and cloud particle backscatter. Both balloons encountered highly variable atmospheric conditions, with periods of intense vertical winds occurring sporadically throughout their flights. Downward winds as large as 3.5 meters per second occasionally forced the balloons to descend as much as 2.5 kilometers below their equilibrium float altitudes. Large variations in pressure, temperature, ambient light level, and cloud particle backscatter (VEGA-1 only) correlated well during these excursions, indicating that these properties were strong functions of altitude in those parts of the middle cloud layer sampled by the balloons.

Sagdeev, R. Z.↗
NASA NTRS1985

Radio phase characteristics of terrain from multipolarized synthetic aperture radar data

Recent advances in digital data acquisition and signal processing technology permit simultaneous measurement of the complex (amplitude and phase) radar backscatter from several polarization-diverse antennas. While absolute phase mesurements remain to be analyzed in detail. The differential phase of signals polarized parallel and perpendicular to the plane of incidence provide information on the scattering mechanisms that dominate the interaction of the radio waves with the terrain. Analysis of phase backscatter maps from a typical urban area yields a bimodal distribution with the two peaks separated by approximately 180 degrees, highly indicative of a dominant simple geometric one bounce-two bounce mechanism. Some maps of agricultural areas exhibit a similar distribution, however, other agricultural areas yield a distribution that, while still bimodal, consists of two peaks separated by about 110 deg. Still other agricultural areas exhibit a more complex distribution. All of the observed phase shifts appear to be independent of incidence angle from at least 20 deg to 55 deg, therefore the 110 degree shifts are inconsistent with both the geometric model used for the urban area and with common dielectric slab models.

Zebker, H. A.↗
NASA NTRS1986

Preliminary evaluation of the SIR-B response to soil moisture, surface roughness, and crop canopy cover

Two predawn ascending data-takes by the Shuttle Imaging Radar-B (SIR-B) were used to evaluate the effects of surface roughness, crop canopy, and soil moisture on radar backscatter. The two images, separated by three days, were both obtained at 30-deg local angle of incidence, but with opposite azimuth viewing directions. The imagery was externally calibrated with respect to the radar backscattering coefficient sigma(0) via response to arrays of point and area-extended targets of known radar cross section. Three land-cover classes: (1) corn, (2) corn stubble and plowed bare soil, and (3) disked bare soil, soybeans, soybean stubble, alfalfa, and clover could be readily separated for either observation date on the basis of image tone alone. The dependence of sigma(0) on the surface roughness and canopy brightness inhibits the capability of SIR to globally estimate the near-surface soil moisture from the value of sigma(0) for single date observations, unless the surface roughness or canopy cover conditions are accounted for. However, within given ranges of these conditions, the sigma(0) was found to be highly correlated with the soil moisture.

Dobson, M. C.↗
NASA NTRS1986

Shuttle Imaging Radar - Physical controls on signal penetration and subsurface scattering in the Eastern Sahara

Interpretation of Shuttle Imaging Radar-A (SIR-A) images by McCauley et al. (1982) dramatically changed previous concepts of the role that fluvial processes have played over the past 10,000 to 30 million years in shaping this now extremely flat, featureless, and hyperarid landscape. In the present paper, the near-surface stratigraphy, the electrical properties of materials, and the types of radar interfaces found to be responsible for different classes of SIR-A tonal response are summarized. The dominant factors related to efficient microwave signal penetration into the sediment blanket include (1) favorable distribution of particle sizes, (2) extremely low moisture content and (3) reduced geometric scattering at the SIR-A frequency (1.3 GHz). The depth of signal penetration that results in a recorded backscatter, here called 'radar imaging depth', was documented in the field to be a maximum of 1.5 m, or 0.25 of the calculated 'skin depth', for the sediment blanket. Radar imaging depth is estimated to be between 2 and 3 m for active sand dune materials. Diverse permittivity interfaces and volume scatterers within the shallow subsurface are responsible for most of the observed backscatter not directly attributable to grazing outcrops. Calcium carbonate nodules and rhizoliths concentrated in sandy alluvium of Pleistocene age south of Safsaf oasis in south Egypt provide effective contrast in premittivity and thus act as volume scatterers that enhance SIR-A portrayal of younger inset stream channels.

Schaber, G. G.↗
NASA NTRS1985

Measurements of atmospheric nitric oxide from Nimbus 7 SBUV ultraviolet spectral scan data

Results are given of SBUV (solar backscattered ultraviolet instrument) measurements from Nimbus 7, when - one day per month - it is operated in a spectral scan mode, scanning from 160 nm to 400 nm in 0.2-nm steps. By measuring the intensity of a series of nitric oxide (NO) gamma band fluorescence features in this wavelength range, it has been possible to estimate the amount of NO in the upper stratosphere and mesosphere. The background of atmospherically scattered sunlight normally masks the much weaker NO gamma band emission, but these emission features are discriminated by subtracting a synthetic spectrum calculated for a model atmosphere that includes only Rayleigh scattering and absorption by ozone and oxygen. The resulting difference plot clearly reveals features resulting from processes not included in the simple model, such as NO gamma band emission. Nitric oxide is inferred by measuring the absolute intensity of various bands relative to the adjacent background and relating this intensity to total NO above an altitude determined by the backscattering contribution function for that band. NO observations near the solstice and at various latitudes are reported.

Mcpeters, R. D.↗
NASA NTRS1985

Nimbus 7 SBUV/TOMS calibration for the ozone measurement

The Solar Backscatter Ultraviolet and Total Ozone Mapping Spectrometer (SBUV/TOMS) onboard the Nimbus 7 satellite is an atmospheric ozone measuring experiment from solar backscattered ultraviolet radiation off the earth atmosphere. The excellent spatial coverage and long lifetime of SUBV/TOMS makes this experiment viable for the long term monitoring of the global ozone. A technique used in the in-orbit calibration of SUBV/TOMS for the ozone data processing is presented. This technique employs a model to explain and correct the observed instrument output due to degradation. From the analyses with the corrected data to verify the model, it is concluded that the in-orbit instrument calibration for the ozone measurement is accurate within 2 percent for the first four years of the instrument operation.

Park, H.↗
NASA NTRS1986

Coherent lidar technology for global wind profiling

Current lidar systems are proven sensors for atmospheric wind measurement. Ground-based and airborne continuous wave and pulsed CO2 systems were developed and applied to several wind measuring applications. Analytical and hardware feasibility studies indicte the feasibility of measuring the global wind field from a space splatform. A Global Backscater Experiment is planned by NASA to develop a global model of aerosol backscatter using a CO2 laser. Ground-based aerosol backscatter profiles will also be obtained using a ruby and a pulsed CO2 lidar.

Huffaker, R. M.↗
NASA NTRS1986

Inversion of 2 wavelength Lidar data for cloud properties

The inversion of the lidar equation to derive quantitative properties of the atmosphere has continued to present considerable difficulty. The results of a study in which Klett's procedure was utilized for the analysis of cloud backscatter measurements made simulataneously at two ruby lidar wavelengths (694nm,347nmm) are presented. With one lidar system a cloud is probed at the two wavelength and the backscatter measured simulataneously by separate receivers. As a result two sigma profiles which should differ only because the wavlength dependence of the scattering. Experimental data presented to demonstrate the effects and the implications of the applications of the inversion method will be discussed.

Pal, S. R.↗
NASA NTRS1986

The usefulness of Klett's inversion algorthms to simulated satellite Lidar returns

The lidar equation is a special form of the radiative transport equation in single scattering approximation and describes the return signal of a lidar. Klett's algorithm for retrieving the total extinction coefficient profile was developed for application to ground-based lidar returns by a backward integration from the far end to the near end, the range where the incident and backscattered pulse overlap totally. The applicability of Klett's algorithm to satellite backscatter lidar returns was assessed. The simulated data of a 1 J Alexandrite laser operated at about 0.7 micron and at a satellite flight level of 840 km.

Kastner, M.↗
NASA NTRS1986

Lidar mapping of a mixture of aerosol concentrations in a varying atmosphere

In several recent applications dealing with lidar measurement of atmospheric pollution, two basic assumptions are made: (1)The investigated aerosol layer is the only particulate material within the scattering volume; and (2)The contribution of the gaseous atmosphere to the lidar backscattering signals can be estimated and deducted from the total backscattering measurements. In the method discussed a generalized method which allows the elimination of the above mentioned assumptions was developed using multiparameter lidar measurements. The different parameters can be several wavelengths, polarization of the scattered light, scattering angles, or any combination of these parameters. The basic requirements are given. The detailed derivations are presented and discussed.

Kleiman, M.↗
NASA NTRS1986

Doppler lidar studies of atmospheric wind field dynamics

For the past 5 years the Wave Propagation Lab. has operated a pulsed CO2 Doppler lidar system to evaluate coherent laser radar technology and to investigate applications of the technique in atmospheric research. The capability of the system to provide measurements of atmospheric winds, backscatter, and water vapor has been extensively studied over this period. Because Doppler lidar can measure atmospheric wind structure in the clear air without degradation by terrain features, it offers a unique capability as a research tool for studies of many transient or local scale atmospheric events. This capability was demonstrated in recent field experiments near Boulder, Colo. and Midland, Tex., in which the lidar clearly depicted the wind field structure associated with several types of phenomena, including thunderstorm microbursts, valley drainage flow, and passage of a dryline front. To improve sensitivity during the periods of low aerosol backscatter, the system has recently been upgraded with new transmitter/receiver hardware. The upgraded system, which transmit 2 J per pulse of output energy at a rate of 50 Hz and incorporates computer control for automated operation, underwent calibration testing during the spring of 1986.

Hardesty, R. M.↗
NASA NTRS1986

Lidar method of measurement of atmospheric extinction and ozone profiles

A description of a method of measurement of atmospheric extinction and of ozone profiles by use of the backscatter signal from a monostatic lidar is given. The central feature of the procedure involves a measurement of the ratio of the Raman backscatter returns of both the oxygen and nitrogen atmospheric content. Because the ratio of the number density of both species is known to high accuracy, the measurement itself becomes a measure of the ratio of two transmissions to altitude along with a ratio of the two system constants. The calibration measurement for determining the value of the ratio of the two system constants or electro-optical conversion constants is accomplished by a lidar measurement of identical atmospheric targets while at the same time interchanging the two optical filters in the two optical channels of the receiver. More details of the procedure are discussed. Factoring this calibrated value into the measured O2/N2 profile ratio provides a measured value of the ratio of the two transmissions. Or equivalently, it provides a measurement of the difference of the two extinction coefficients at the O2 and N2 Raman wavelengths as a function of the height.

Cooney, J. A.↗
NASA NTRS1986

Lidar observations of the decline of the El Chichon stratospheric load

The eruption of the Mexican volcano El Chichon in Apr. 1982 enhanced the stratospheric aerosol load to a level which so far has not been observed by remote sensing techniques. The ruby lidar system at Garmisch-Partenkirchen recorded an increase of about two orders of magnitude above the background level of the years 1977/78. At northern midlatitudes backscattering was peaking in Jan./Feb. 1983, as illustrated. The decline of the El Chichon stratospheric perturbation is discussed. The decay of the El Chichon stratospheric cloud is characterized by an overall 1/e lifetime of about 12 months. The El Chichon decay is further characterized by seasonal variations of the integral backscattering coefficient, which exhibit a winter maximum and a summer minimum. These variations are inversely correlated with the seasonal mean movement of the tropopause height indicating transport processes.

Jaeger, H.↗
NASA NTRS1986

Lidar measurements of thermal structure

Rayleigh backscatter observations at 532 nm and 355 nm of relative atmospheric density above Aberystwyth on a total of 93 nights between Dec. 1982 and Feb. 1985 were used to derive the height variation of temperature in the upper stratosphere and mesosphere. Preliminary results for height up to about 25 km were also obtained from observations of Raman backscattering from nitrogen molecules. Comparisons were carried out for stratospheric heights with satellite borne measurements; good agreement was found between equivalent black body temperatures derived from the lidar observations and those obtained from nadir measurements in three channels of the stratosphere sounder units on NOAA satellites; the lidar based atmospheric temperatures have shown general agreement with but a greater degree of structure than the limb sounding measurements obtained using the SAMS experiment on the NOAA-7 satellite. In summer, stratospheric and mesospheric temperatures showed a smooth height variation similar to that of the CIRA model atmosphere. In contrast, the winter data showed a great variability with height, and marked temperature changes both from night to night and within a given night.

Jenkins, D. B.↗
NASA NTRS1985

Characterization and Discrimination of Selected Vegetation Canopies from Field Observations of Bidirectional Reflectances

A full evaluation of the bidirectional reflectance properties of different vegetated surfaces was limited in past studies by instrumental inadequacies. With the development of the PARABOLA, it is now possible to sample reflectances from a large number of view angles in a short period of time, maintaining an almost constant solar zenith angle. PARABOLA data collected over five different canopies in Texas are analyzed. The objective of this investigation was to evaluate the intercanopy and intracanopy differences in bidirectional reflectance patterns. Particular attention was given to the separability of canopy types using different view angles for the red and the near infrared (NIR) spectral bands. Comparisons were repeated for different solar zenith angles. Statistical and other quantitative techniques were used to assess these differences. For the canopies investigated, the greatest reflectances were found in the backscatter direction for both bands. Canopy discrimination was found to vary with both view angle and the spectral reflectance band considered, the forward scatter view angles being most suited to observations in the NIR and backscatter view angles giving better results in the red band. Because of different leaf angle distribution characteristics, discrimination was found to be better at small solar zenith angles in both spectral bands.

Donovan, Sheila↗
NASA NTRS1986

Radar scene generation for tactical decision aids

The Mueller matrix and polarization covariance matrix for polarimetric radar systems was studied. The clutter was modeled by a layer of random permittivity, described by a three-dimensional correlation function, with variance, and horizontal and vertical correlation lengths. This model was applied, using the wave theory with Born approximations carried to the second order, to find the backscattering elements of the polarimetric matrices. Theoretical predictions are matched with experimental data for vegetation fields. The strong fluctuation theory was used to derive the backscattering cross sections. A two-layer anisotropic random medium model was developed for the active and passive microwave remote sensing of ice fields. A three-layer random medium model was adopted to study the volume scattering effects for the active and passive microwave remote sensing of snow-covered ice fields.

Kong, J. A.↗
NASA NTRS1986

Imaging radar contributions to a major air-sea-ice interaction study in the Greenland Sea

By virtue of the Synthetic Aperture Radar (SAR's) imaging capabilities, such as all-weather imaging, relatively high resolution, and large dynamic range of backscatter from SAR ice and open ocean, information on the important marginal ice zone (MIZ) parameters can be derived from the SAR data. Information on ice edge location and location of ice-edge eddies, for example, can be obtained directly from examination of the imagery as can detection of ocean fronts and internal waves. With machine-assisted manual image analysis, estimates of ice concentration, floe size distributions, and ice field motion can also be derived. Full digital analysis, however, is required to obtain gravity wave spectral information and backscatter statistics for ice type discrimination and automated ice concentration algorithms.

Shuchman, Robert A.↗
NASA NTRS1986

Multiple incidence angle SIR-B experiment over Argentina

The Shuttle Imaging Radar (SIR-B), the second synthetic aperture radar (SAR) to fly aboard a shuttle, was launched on October 5, 1984. One of the primary goals of the SIR-B experiment was to use multiple incidence angle radar images to distinguish different terrain types through the use of their characteristic backscatter curves. This goal was accomplished in several locations including the Chubut Province of southern Argentina. Four descending image acquisitions were collected providing a multiple incidence angle image set. The data were first used to assess stereo-radargrammetric techniques. A digital elevation model was produced using the optimum pair of multiple incidence angle images. This model was then used to determine the local incidence angle of each picture element to generate curves of relative brightness vs. incidence angle. Secondary image products were also generated using the multi-angle data. The results of this work indicate that: (1) various forest species and various structures of a single species may be discriminated using multiple incidence angle radar imagery, and (2) it is essential to consider the variation in backscatter due to a variable incidence angle when analyzing and comparing data collected at varying frequencies and polarizations.

Cimino, Jobea↗