Showing papers in "IEEE Transactions on Geoscience and Remote Sensing in 1975"

Fading Characteristics of Panchromatic Radar Backscatter from Selected Agricultural Targets

Abstract: An experiment was performed to determine the fading characteristics of backscattered radar signals from four agricultural targets at 9 GHz. The targets included two different row crops (corn and soybeans), a continuous canopy (alfalfa) and bare ground. After a short review of the statistics of Rayleigh fading backscatter, the data processing method and the results of the experiment are analyzed. Comparison with theory shows adequate agreement with the experimental results provided crop type, soil moisture condition and incidence angle are correctly incorporated in the target model. Because recent studies indicate that a high degree of precision is required for mapping vegetotion types with radar, it is necessary to acquire as much a priori knowledge of target fading characteristics as possible.

The McIdas System

Abstract: A Man-Computer Interactive Data Access System (McIDAS) has been developed for image processing and analysis. The hardware and software design of McIDAS is outlined with specific regards to the meteorological user. A variety of image processing techniques have been implemented on McIDAS for use with many kinds of images, in particular, ATS, ERTS-A, Mariner X, and SMS-A satellite data. A flexible digital image enhancement system is included in the McIDAS design. Special mention is made of the NAVIGATION, WINDCO, and CLDHGT systems which were developed for the purpose of aligning time sequences of geosynchronous satellite pictures, and determining the motion and height of selected cloud targets. The support which McIDAS can provide to the TV broadcasting community is also discussed.

Crosswind Measurements through Pattern Recognition Techniques

Abstract: Optical devices currently used for crosswind measurements are calibrated and results interpreted on the basis of theoretical predictions. However, under strong turbulence conditions, the experimental observations do not compare well with the theoretical predictions. This deficiency can be overcome by use of a learning machine which utilizes a pattern recognition technique. Basically this approach substitutes observed experience for a detailed knowledge of the physical model. The technique utilizes a minicomputer to process observed spectral profiles. In the training phase spectral features, which are weakly intercorrelated but strongly correlated with the crosswind, are selected and classified with known winds. These data are stored in the machine. During the execution phase, the observed spectral features are compared with the previously stored classifications to yield a best estimate of the crosswind. Experimental results are presented which quantify the performance of this method.

SA Tellite Doppler Data Processing for Platform Navigation

Abstract: The NIMBUS Meteorological Satellite will carry a system designed to receive electronic platform signals. The Doppler data is processed to provide estimates of their location and velocity. The current system provides for a location estimation accuracy of about 1 KM and component velocity estimation accuracy of about 1 M/S. The estimates, however, can be perturbed by various suspected noise sources. These effects are assessed to provide a measure of robustness of the estimation process.

In Situ Measurement of Marine Sediment Acoustical Properties during Coring in Deep Water

Abstract: In order to obtain in situ measurements, to several meters depth in a marine sediment, of compressional wave speed and attenuation, a device has been built for attachment to ocean bottom sediment corers. This profilometer consists of transducers on the lower end of the coring tool which are connected by armored cables to an electronics package on the upper end of the tool, thus allowing acquisition of acoustical data with a minimum of modification to a standard corer. Early measurements with a prototype profilometer, which required electrical cables to the surface, established the accuracy and usefulness of the technique. The new deep water version of the profilometer is self contained including provisions for recording the data in the electronics package on the corer. Design operating water depth for the new system is 5 km. Test results for the new profilometer are presented including several high resolution in situ sound speed profiles to 12 m depth in deep water (4.5 km) sediments. Detailed layering is described including a high strength, high water content layer, several thin high speed sand layers, and several low speed layers. The data indicate that the near surface low speed zone in these sediments is composed of several thin low speed layers imbedded in a higher speed matrix.

The Nimbus F Random Access Measurement System (RAMS)

Abstract: In 1974, the Random Access Measurement System (RAMS) will be launched aboard the NIMBUS F satellite as part of the Tropical Wind, Energy Conversion, and Reference Level Experiment (TWERLE). This paper describes operation and performance of the RAMS instrument, which will provide a means of tracking and collecting data from a large number of instrumented platforms. In operation, the RAMS will perform satellite onboard processing of up to eight simultaneous platform transmissions, following search and detection of the randomly received platform transmissions in a compressed-time expanded-frequency domain. The processed data is stored aboard the satellite for readout every 108 minutes (orbital period), and platform locational coordinates and/or velocity components are determined in a central ground data processing facility. TWERLE system performance design goals are ±5 km position location, ±1 meter/second velocity determination, and 1000 platforms/orbit multiple access accommodation.

The Applications of McIdas

Abstract: The Man-computer Interactive Data Access System (McIDAS) is a combination of hardware and software developed for processing image data from high volume data sources such as satellites. This paper describes the use of McIDAS. Key features of McIDAS are: color television display with capability for rapid (up to 30 frames/sec) sequencing of set of images, analog and digital data storage, interactive data processing and display control, data flow and processing controlled by computer software, data processing by accessing subsets of data. Uses of McIDAS include: measuring cloud velocities from geosynchronous satellites, calibrating cloud pictures for rain from radar, classifying land use from ERTS images, assembling weather data for public broadcast.

A Note on Brightness Temperature at Millimeter Wavelengths

Abstract: The first-order correction to the approximate proportionality between the brightness temperature and the specific intensity of radiation which is usually assumed to hold in the near earth environment at microwave frequencies is examined. Corrections as large as 7°K in the vicinity of 300 GHz are shown to be required. It is shown that the influence of this correction can be incorporated into solutions of the low frequency form of the radiative transfer equation simply by a change in the boundary conditions describing the downward flowing flux at the top of the earth's atmosphere.

The Twerle Balloon-to-Satellite Data Transmitting System

Abstract: This paper describes the balloon instrumentation system which provides the one-way link for data gathering and navigation in the Tropical Wind, Energy conversion and Reference Level Experiment (TWERLE). In this experiment 400 instrumented constant-level balloons will be launched at the southern hemisphere during 1975. The Random Access Measurement System (RAMS) on board the NIMBUS-F satellite, will comprise the receiving end of the link. The data encoder, stable oscillator, transmitter and antenna are described, as well as two supporting components, the power source and the magnetic cutdown. These six items weigh 850 g. The oscillator-transmitter consume 1.9 W dc power to provide 0.6 W phase modulated RF power. Standby dc power consumption is 0.3 W.

A Buoy Transmit Terminal for the Nimbus-F Satellite

Abstract: The overall Buoy Transmit Terminal (BTT) to Nimbus-F Satellite, RAMS (Random Access Measurement System) concept is examined. This system provides a dual position fixing and communication function. A general approach to meeting the BTT requirements is discussed. The paper continues with a discussion of the development of the various BTT elements which make it ideally suited for placement on-board buoys with small payloads. Sample performance parameters, derived from test data, are presented to provide a measure of familiarity with the BTT and its applications.

Platform Location and Data Collection by Satellite Systems the EOLE Experiment

Abstract: A technical description of the EOLE location and data collection system with 480 constant level balloons released in the Southern Hemisphere is presented : the EOLE satellite contacts successively each platform, acquires and stores range and range rate data allowing computation of the location of each transponder and meteorological data measured by the plat form sensors. This information is stored on board and then read out by telemetry upon reception of a command from ground stations. The experiment itself is described and the main technical results are analyzed ; the ultimate location accuracy of the EOLE System was found to be of the order of 300 meters for fixed platforms but, some difficulties concerning the Location of drifting balloons were encountered due to the necessity of compensating the Doppler shift for platform motion. The main scientific results are briefly presented as well as some post-EOLE experiments. Future developments of this type of location and data collection system are described as a conclusion.

Raw Data Digitizing and Recording System for the Omega-Sonde Wind Finding Ground Station

Abstract: This paper describes a low cost Omega-sonde data acquisition system consisting of a portable shipboard raw data recording package and a minicomputer interface used in the data reconstruction. The Omega phase is detected against a crystal controlled reference signal. The detected relative phase is recorded in digital form using timing signals controlled by the same crystal oscillator. The meteorological information is recorded in analog form. The data are stored on two-track audio tape cassettes which are processed via the interface and a minicomputer to yield IBM compatible computer tapes. The interface converts both the phase and the meteorological data to parallel-bit format. The recorded meteorological data (frequency) is counted and digitized using a clock signal which is phase-locked to the recorded phase data timing signal. The effects of tape wow and flutter on the meteorological data are thus reduced considerably. Samples of recovered phase and meteorological data are included.

Superpressure Balloons and Communications Satellites - A New Approach for Tropical Meteorological Soundings

Abstract: A new approach for measuring winds, temperature and humidity in the tropics has been developed which utilizes high-altitude superpressure balloons and a communications or data-collection satellite for data relay. A large balloon is used to carry a load dropsondes which are individually released upon command from a synchronous satellite. These sondes telemeter Omega navigation signals, temperature and humidity data to the mother balloon which also serves as a data relay terminal to a synchronous satellite. The satellite in turn transmits the data to a ground station. Upon reception the data are processed in a large computer to recover the meteorological measurements. The National Center for Atmospheric Research is sponsored by the National Science Foundation.

Measurement of Sea State by RF Interferometry

Abstract: The mutual coherence function is derived for the scattered field due to a plane wave incident on the surface of the sea. The analysis is based on first order small perturbation theory, and neglects composite surface effects. The concept of an interferometer measuring the space correlation function of the scattered field providing information leading to the determination of the wave number spectrum of the sea surface is demonstrated. Assuming that the sea has a Phillips spectrum with a low cutoff number determined by the wind, a number of the basic physical properties of the proposed device are examined.

Meteorological Forecast Applications Associated with AFOS

Abstract: The primary interface between the AFOS system and the National Weather Service (NWS) forecaster lies within the area of meteorological forecast applications. Although AFOS will benefit the present system in many ways, it will also allow for new applications and different packaging of guidance material. Two such efforts are now in progress. The first of these concerns the automatic monitoring and updating of aviation terminal weather forecasts. Specifically, the AFOS system minicomputer will be programmed to compare each surface observation with the terminal forecast and determine if a problem or a potential problem exists. If so, a message will be automatically generated which will alert the forecaster to the situation and provide him with an objective forecast of ceiling and visibility. The second effort concerns the generation and updating of computer-worded public forecasts. The initial forecast, along with a guidance matrix, will be generated centrally and transmitted via the National Distribution Circuit to the forecast office. The forecaster can accept the forecast as is, make minor changes through text editing the message, or make major changes. Updating to include major revisions requires that the forecast be regenerated, this time on the local AFOS minicomputer.

AFOS Experimental Program

Abstract: The experimental program to date has concentrated on the forecaster's work station. By presenting field forecasters with a simulated problem, we were able to identify several important features to be enhanced and several to be changed. The most important feature to be enhanced was the flexibility in creating individual work stations. Smaller units, with specialized func-tions, that could be linked together in various combi, nations, appear to be highly desirable. The forecast preparation function was indentified as the most critical for design of the work station. This function places more emphasis on alphanumeric (KCRT) and message composition devices than on graphic displays. The use of KCRT devices for forecast preparation has several advantages including cost. Beyond the technical details of the work station, we learned much about the idiosyncrasies of the forecasters. A significant number wear bifocals, for example, and the orientation of displays is particularly important. The development of one horizontal keyboard for all hardware control functions is another change to be considered. From the field forecasters we also gained insight into the training required. The mechanics of AFOS are easily learned, but adaption into forecasters' work routines will be more difficult. However, considering the high skill level of National Weather Service field people, "overkill" on training should be avoided. The local data base needs to be enhanced. To this end, the parallel programs leading to automating surface, radar and upper air observations are being interfaced with AFOS.

A Difference Potential Method for Induction Sondes

Abstract: The response of a general induction sonde in a heterogeneous formation is computed using a difference potential technique. This difference potential method effectively transforms the source coil singularities into a continuum of finite sources distributed throughout the formation. The resulting equations are solved via finite-difference techniques. The apparent conductivity responses are corroborated by the solutions of an integral equation formulation for two invaded thin bed examples and a homogeneous formation example.

A Solid-State Digital Tide Gauge

Abstract: A new type of marine water-height sensing device has been designed and built for use as a tide gauge Primary prerequisites for the instrument were inexpensive construction, avoidance of moving parts, reliability of operation in a marine environment, and direct computer interface for automated data acquisition The resultant instrument employs carbon electrodes fixed to a polyvinyl chloride pipe, and remote electronics to sense water level in the pipe The electronics were designed so as to minimize current through the electrodes The design is adaptable to different tidal ranges and resolutions, and could also be used as a wave-height sensor

A Hybrid Computer Time Code Reader Used to Digitize Sounding Rocket Data

Abstract: A technique is described for utilizing a hybrid computer as a time code reader and digitizer. The NASA 36-bit time code is an absolute time reference for digitizing analog signals to 1 mV resolution at a 1 kHz sampling rate. The analog computer circuit and the operation of the merged analog and digital computer systems is described. A result of this digitization process applied to analog signals recorded on magnetic tape during an Auroral sounding rocket flight is given as an example. This is a general technique that could be applied to other areas such as geology, meteorology, oceanography, and seismology.