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NASA NTRS1985

The Venus Balloon Project

During the Soviet Vega Mission to Venus and Comet Halley, two instrumented balloons will be placed into the Venusian atmosphere in June 1985. These Soviet/French balloons will be used to study the structure and dynamics of the Venusian atmosphere by means of in situ measurements and earth-based VLBI determination of balloon position and velocity. The DSN 64-meter subnet will be part of an international network of antennas organized by the French to support this mission. The DSN is installing new L-band receiving systems for this task. All scientific data from the balloons will be analyzed by a joint Soviet/French/U.S. science team.

Preston, R. A.↗

NASA NTRS1983

Analysis of data acquired by synthetic aperture radar and LANDSAT Multispectral Scanner over Kershaw County, South Carolina, during the summer season

Data acquired by synthetic aperture radar (SAR) and LANDSAT multispectral scanner (MSS) were processed and analyzed to derive forest-related resources inventory information. The SAR data were acquired by using the NASA aircraft X-band SAR with linear (HH, VV) and cross (HV, VH) polarizations and the SEASAT L-band SAR. After data processing and data quality examination, the three polarization (HH, HV, and VV) data from the aircraft X-band SAR were used in conjunction with LANDSAT MSS for multisensor data classification. The results of accuracy evaluation for the SAR, MSS and SAR/MSS data using supervised classification show that the SAR-only data set contains low classification accuracy for several land cover classes. However, the SAR/MSS data show that significant improvement in classification accuracy is obtained for all eight land cover classes. These results suggest the usefulness of using combined SAR/MSS data for forest-related cover mapping. The SAR data also detect several small special surface features that are not detectable by MSS data.

Wu, S. T.↗

NASA NTRS1984

Earth resources research using the Shuttle Imaging Radar system

The Shuttle Imaging Radar (SIR) is an L-band synthetic radar that transmits and receives horizontally polarized microwave radiation. It was originally launched on the second Shuttle test flight (STS-2) in November 1981 with the antenna depression angle fixed at 43 deg. In this configuration, the radar system was referred to as SIR-A, and it collected more than then a million square kilometers of Earth imagery in a variety of areas situated between 38 deg north and south latitude. SIR-A data was optically recorded onboard the Shuttle, and it was subsequently correlated on the ground to produce imagery with a 50 kilometer swath width and a surface resolution of approximately 40 meters. The SIR is presently being upgraded into a new configuration termed SIR-B, in which the radar's antenna can be mechanically rotated in the Shuttle's payload bay during an orbital mission. SIR-B is currently scheduled for flight on the seventeenth Shuttle mission (STS-17) that is tentatively planned for August 1984. In its new configuration, the SIR-B can be used to image selected regions at different angles of incidence ranging from 15 deg to 60 deg (as measured from the local vertical). In principle, multiple incidence angle radar imagery of selected areas can be coregistered and used to differentiate surficial materials on the basis of their roughness characteristics. This procedure is conceptually similar to the use of multispectral imagery acquired at shorter wavelengths to discriminate surficial materials on the basis of their pigmentation.

Monson, R.↗

NASA NTRS1985

Propagation considerations in land mobile satellite transmission

It appears likely that the Land Mobile Satellite Services (LMSS) will be authorized by the FCC for operation in the 800 to 900 MHz (UHF) and possibly near 1500 MHz (L-band). Propagation problems are clearly an important factor in the effectiveness of this service, but useful measurements are few, and produced contradictory interpretations. A first order overview of existing measurements is presented with particular attention to the first two NASA balloon to mobile vehicle propagation experiments. Some physical insight into the interpretation of propagation effects in LMSS transmissions is provided.

Vogel, W. J.↗

NASA NTRS1984

A 406 MHz geostationary satellite SARSAT experiment

A 406 MHz SARSAT experiment using the GOES system to demonstrate the utility of integrating a near-instantaneous distress alerting capability achievable by the geostationary satellites with the location capability of the low altitude, near-polar orbiting satellite system is described. Tests include the evaluation of technical performance of a variety of maritime, aviation, and land-based SARSAT beacons under operational environment conditions as well as a demonstration of system effectiveness in pseudo real distress incident situations. The technical performance tests parallel the CCIR coordinated trials program conducted at L-band frequencies using the INMARSAT satellites. Tests, including schedules, are outlined.

Friedman, M. L.↗

NASA NTRS1985

Second-generation mobile satellite system. A conceptual design and trade-off study

In recent years, interest has grown in the mobile satellite (MSAT) system, a satellite-based communications system capable of providing integrated voice and data services to a large number of users. To explore the potential of a commercial mobile satellite system (MSS) beyond the horizon of the first generation, using technologies of the 1990's and to assist MSAT-X in directing its efforts, a conceptual design has been performed for a second-generation system to be launched around the mid-1990's. The design goal is to maximize the number of satellite channels and/or minimize the overall life-cycle cost, subject to the constraint of utilizing a commercial satellite bus with minimum modifications. To provide an optimal design, a series of trade-offs are performed, including antenna sizing, feed configurations, and interference analysis. Interference is a serious problem for MSAT and often an overlapping feed design is required to reduce interbeam interference. The trade-off studies will show that a simple non-overlapping feed is sufficient for the second-generation system, thus avoiding the need for the complicated beam-forming network that is associated with the overlapping feed designs. In addition, a system that operates at L-band, an alternative frequency band that is being considered by some for possible MSAT applications, is also presented.

Sue, M. K.↗

NASA NTRS1984

Characterizing land processes in the biosphere

NASA long-term planning for the satellite remote sensing of land areas is discussed from the perspective of a holistic interdisciplinary approach to the study of the biosphere. The earth is characterized as a biogeochemical system; the impact of human activity on this system is considered; and the primary scientific goals for their study are defined. Remote-sensing programs are seen as essential in gaining an improved understanding of energy budgets, the hydrological cycle, other biogeological cycles, and the coupling between these cycles, with the construction of a global data base and eventually the development of predictive simulation models which can be used to assess the impact of planned human activities. Current sensor development at NASA includes a multilinear array for the visible and IR and the L-band Shuttle Imaging Radar B, both to be flown on Shuttle missions in the near future; for the 1990s, a large essentially permanent man-tended interdisciplinary multisensor platform connected to an advanced data network is being planned.

Erickson, J. D.↗

NASA NTRS1984

Utilization of vegetation indices to improve microwave soil moisture estimates over agricultural lands

A technique is presented by means of which visible/near-IR data are used to develop corrections in remotely sensed microwave soil moisture signals, in order to account for vegetation effects. Visible/IR data collected with the NASA NS001 Thematic Mapper Simulator were used to calculate the Perpendicular Vegetation Index (PVI), which was then related to the change of sensitivity of the microwave measurement to surface soil moisture. Effective estimation of soil moisture in the presence of vegetation can be made with L-band microwave radiometers and visible/IR sensors when the PVI is lower than 4.3. This technique offers a means for the estimation of moisture from a space platform over many agricultural areas, without expensive ground data collection.

Theis, S. W.↗

NASA NTRS1984

Interpretation and modeling of quasiperiodic diffraction patterns observed in equatorial VHF scintillation due to plasma bubbles

Quasiperiodic diffraction patterns have been observed in VHF scintillation recorded at Ascension Island in 1981. The patterns occur most often at the beginning or end of a scintillation patch and are shown to be consistent with those expected from irregularities having east-west scale sizes of a few hundred meters that are associated with the walls (edges) of equatorial plasma bubbles. By adjusting the geophysical parameters in a computer simulation of the amplitude fluctuations expected simultaneously at VHF, L-Band and C-Band, we model a specific event in detail. The model contains information on the size and strength of the structures that cause the regular fading patterns. In addition, multi-frequency diffraction patterns are computed for a 'phase screen' model based on high resolution measurements of a structured plasma bubble wall made using the AE-E satellite. The results are qualitatively very similar to the observations. Finally, implications of the model results for the extraction of information about the vertical structure of the irregularities are discussed.

Franke, S. J.↗

NASA NTRS1985

Brief search for low-mass objects

Observations of the nearby white dwarfs EG 5 (van Maanen 2) and EG 290 obtained in the J, H, K, L, L-prime, and M bands using an RC1 photometer at the Cassegrain focus of the 3.3-m IR telescope at Mauna Kea on Dec. 2, 1983 are reported. The L-band fluxes are analyzed to search for low-mass companion objects, but none is found. Upper limits of Te = 850 K and L = 5 x 10 to the -6th solar luminosity are established for the putative companions of both dwarfs, corresponding to a mass of 0.027 solar mass or less for an age of 3 Gyr.

Krishna Kumar, C.↗

NASA NTRS1985

Microwave inversion of leaf area and inclination angle distributions from backscattered data

The backscattering coefficient from a slab of thin randomly oriented dielectric disks over a flat lossy ground is used to reconstruct the inclination angle and area distributions of the disks. The disks are employed to model a leafy agricultural crop, such as soybeans, in the L-band microwave region of the spectrum. The distorted Born approximation, along with a thin disk approximation, is used to obtain a relationship between the horizontal-like polarized backscattering coefficient and the joint probability density of disk inclination angle and disk radius. Assuming large skin depth reduces the relationship to a linear Fredholm integral equation of the first kind. Due to the ill-posed nature of this equation, a Phillips-Twomey regularization method with a second difference smoothing condition is used to find the inversion. Results are obtained in the presence of 1 and 10 percent noise for both leaf inclination angle and leaf radius densities.

Lang, R. H.↗

NASA NTRS1985

NASA/JPL Aircraft SAR Workshop Proceedings

Speaker-supplied summaries of the talks given at the NASA/JPL Aircraft SAR Workshop on February 4 and 5, 1985, are provided. These talks dealt mostly with composite quadpolarization imagery from a geologic or ecologic prespective. An overview and summary of the system characteristics of the L-band synthetic aperture radar (SAR) flown on the NASA CV-990 aircraft are included as supplementary information. Other topics ranging from phase imagery and interferometric techniques classifications of specific areas, and the potentials and limitations of SAR imagery in various applications are discussed.

Donovan, N.↗

NASA NTRS1985

Potential applications of multipolarization SAR for pine plantation biomass estimation

This study was conducted as a part of the research tasks under the Radar Land Cover Analysis Program. The Radar Land Cover Analysis objective is, through utilization of multisensor data, to gain a basic understanding of the measurements and data characteristics in the visible-IR-microwave regions of the electromagnetic spectrum associated with specific surface features and cover types. Since the results of analysis of data acquired by Shuttle Imaging Radar (SIR-A) and LANDSAT Thematic Mapper (TM) over the study area were reported (NSTL/ERL Report No. 228, December 1984), this study focused on the analysis and evaluation of the L-band multipolarization airborne SAR data acquired over a southeastern pine forest scene. The data acquisition mission was flown on September 8 and 9, 1983. The HH, HV polarizations and the VV, VH polarizations were used on the first and the second day, respectively. Due to instrumentation difficulties, the digital recorder recorded only the second day's data. Because of this, only the VV and VH polarization data were used in this analysis. However, the HH and HV polarization images were available for visual comparison. It appears that SAR digital numbers correlate with the index of green biomass.

Wu, S. T.↗

NASA NTRS1985

Vegetation canopy discrimination and biomass assessment using multipolarized airborne SAR

Multipolarized airborne Synthetic Aperture Radar (SAR) data were acquired over a largely agricultural test site near Macomb, Illinois, in conjunction with the Shuttle Imaging Radar (SIR-B) experiment in October 1984. The NASA/JPL L-band SAR operating at 1.225 GHz made a series of daily overflights with azimuth view angles both parallel and orthogonal to those of SIR-B. The SAR data was digitally recorded in the quadpolarization configuration. An extensive set of ground measurements were obtained throughout the test site and include biophysical and soil measurements of approximately 400 agricultural fields. Preliminary evaluation of some of the airborne SAR imagery indicates a great potential for crop discrimination and assessment of canopy condition. False color composites constructed from the combination of three linear polarizations (HH, VV, and HV) were found to be clearly superior to any single polarization for purposes of crop classification. In addition, an image constructed using the HH return to modulate intensity and the phase difference between HH and VV returns to modulate chroma indicates a clear capability for assessment of canopy height and/or biomass. In particular, corn fields heavily damaged by infestations of corn borer are readily distinguished from noninfested fields.

Ulaby, F. T.↗

NASA NTRS1985

Propagation considerations in land mobile satellite transmission

Vogel, W. J.↗

NASA NTRS1985

Passive microwave soil moisture research

The AgRISTARS Soil Moisture Project has made significant progress in the quantification of microwave sensor capabilities for soil moisture remote sensing. The 21-cm wavelength has been verified to be the best single channel for radiometric observations of soil moisture. It has also been found that other remote sensing approaches used in conjunction with L-band passive data are more successful than multiple wavelength microwave radiometry in this application. AgRISTARS studies have also improved current understanding of noise factors affecting the interpretability of microwave emission data. The absorption of soil emission by vegetation has been quantified, although this effect is less important than absorption effects for microwave radiometry.

Schmugge, T. J.↗

NASA NTRS1985

Forest discrimination with multipolarization imaging radar

The relations between polarization signatures and biophysical characteristics through a range of different forest environments were investigated using airborne synthetic-aperture (SAR) images acquired at L-band on March 1, 1984 in South Carolina. SAR data acquired in four linear polarization states with 10-m spatial resolution were encoded as color composite images and compared to US Forest Service forest stand data. The most useful correlative forest data were stand basal area, forest age, site condition index, and forest management type. It is found that the multipolarization images discriminate variation in tree density or difference in the amount of understory, but no evidence has been found for discrimination between evergreen and deciduous forest types.

Ford, J. P.↗

NASA NTRS1985

Electronically Steered Thinned Array Radiometer (ESTAR) system design, calibration, and sensitivity

The ESTAR system, an imaging L-band radiometer designed to provide measurements of soil moisture from space, is described. The large aperture size dictated by the resolution requirement (10 km or less) suggests the use of aperture synthesis, and plans to have ESTAR operate in low earth orbit require that the synthesis be performed in the short data acquisition time permitted by satellite motion. Two forms of ESTAR are described. ESTAR-0 is to be an airborne prototype designed for proof of concept; it will image a line of eight adjacent pixels with 8 degree spatial resolution of 0.1 degree Kelvin temperature resolution, given 1 sec integration time. ESTAR-1 is the satellite version to operate from space. A tentative sensor design will image a line of 128 0.5 degree pixels with 2.0 degree K resolution assuming 0.7 sec integration at 700 km altitude.

Ruf, C.↗