SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Design synthesis and performance analysis (DSPA) program package is collection of subroutines used for computation of design and performance characteristics of viable solar-array-charged battery powered system for flashing-lamp buoys employed as maritime aids to navigation.
A prototype in situ system for monitoring the levels of fecal coliforms in shallow water bodies was developed and evaluated. This system was based on the known relationship between the concentration of the coliform bacteria and the amount of hydrogen they produce during growth in a complex organic media. The prototype system consists of a sampler platform, which sits on the bottom; a surface buoy, which transmits sampler-generated data; and a shore station, which receives, displays the data, and controls the sampler. The concept of remote monitoring of fecal coliform concentrations by utilizing a system based on the electrochemical method was verified during the evaluation of the prototype.
The surface observations used for direct comparison with Seasat-derived values at fixed locations and as input to analyzed fields of pressure, wind, air and sea temperatures, and surface dew point are discussed. These included measurements made by research vessels participating in the Gulf of Alaska Seasat Experiment (GOASEX) and NOAA research platforms in addition to aircraft observations and reports from the World Weather Watch. The application of these observations in describing the synoptic-scale winds over the ocean is discussed, and the sensitivity of the verification statistics to the type of data (observations from buoys, weather ships, and transient vessels with or without anemometers) is considered. Results of a preliminary comparison of wind fields derived from Seasat-A scatterometer observation with winds specified by several types of platforms are presented.
Six algorithms for extracting significant wave height from Geos 3 altimeter data have been compared using simulated Geos 3 data for a single long pass including a variety of sea states and for short segments in the vicinity of NOAA data buoys. The study included algorithms reported by Walsh (1979), Rufenach and Alpers (1978), Gower (1979), Godbey (1965), Fedor (1978) and a real-time model (Miller and Hayne, 1972). Individual differences in results obtained by the algorithms were small, and calculations were found to be in good agreement with surface truth data.
The microwave brightness temperature measurements from the electrically scanned microwave radiometer (frequency = 37 GHz) are compared with oceanic wind measurements from data buoys. It is shown that the brightness temperature can be manipulated to yield a measure of the surface roughening, which can be very well accounted for by a simple geometric optics model. The data of Hollinger (1971) at 1.4, 8, 36, and 19.34 GHz were similarly manipulated and shown to require a surface with less slope variance than that predicted by the Cox and Munk (1955) optical measurements. It is also shown that the surface may be treated as isotropic to an accuracy equivalent to the roughening produced by a 2-m/s wind speed increment.
An oceanic wave measured system is disclosed wherein wave height is sensed by a barometer mounted on a buoy. The distance between the trough and crest of a wave is monitored by sequentially detecting positive and negative peaks of the output of the barometer and by combining (adding) each set of two successive half cycle peaks. The timing of this measurement is achieved by detecting the period of a half cycle of wave motion.
Synthetic aperture radar images of ocean waves were obtained in conjunction with reference wave data near Marineland, Florida, December 14, 1975. Each of the various types of measurements were processed into a form that allowed direct comparisons with the others. Maxima of radar spectra occurred at the same frequencies as the maxima of reference wave height spectra. In a comparison of a radar spectrum with observed spectra of wave height, wave orbital velocity, and surface slope the high-frequency portion of the radar spectrum lay near and between the wave height and the orbital velocity spectra but differed significantly from the surface slope spectrum. The radar-derived mean directions and model-fitted directional spreads of wave energy were close to the values from a directional wave buoy and indicated the accuracy of radar measurements of wave direction. However, a directional plot of a radar spectrum near shore at the frequency of the maximum showed a sharper peak than such a plot of a fitted spectrum derived from reference data.
The United States Coast Guard is developing AIREYE, an all weather, day/night airborne surveillance system, for installation aboard future medium range surveillance aircraft. As part of this program, a series of controlled tests were conducted off southern California to evaluate the oil slick detection capabilities of two Motorola developed, side looking radars. The systems, a real aperture AN/APS-94D and a synthetic aperture coherent on receive (COR) were flown over the Santa Barbara Channel on May 19, 1976. Targets imaged during the coincident overflights included natural oil seepage, simulated oil spills, oil production platforms, piers, mooring buoys, commercial boats and barges at other targets. Based on an analysis of imagery from the coincident radar runs, COR provides better detection of natural and man made oil slicks, whereas the AN/APS-94D consistently exhibited higher surface target detection results. This and other tests have shown that active microwave systems have considerable potential for aiding in the detection and analysis of surface oil accumulations.
SAR imagery obtained by Seasat in the Sargasso Sea during 1978 is examined for cold ring signatures. One orbit on August 26 is thought to have imaged the edge of a cold ring, although the ring's position was not well known at the time. During another orbit on September 23, drifting buoy and expendable bathythermography data furnished conclusive evidence that the ring was centered directly in the SAR swath. Although some suggestive patterns are visible in the images, it is not clear that cold rings can be identified by SAR, even though dynamically similar features, such as the Gulf Stream and warm rings, can be accurately detected. The suggestion is made that cold rings may be imaged inadequately because of their lack of surface temperature gradient.
An upwelling episode in the Point Sal region of the central California coast is examined by using data obtained by a data buoy. The episodes was interrupted by the abrupt abatement of the strong wind which promotes coastal upwelling. The mean hourly upwelling index is calculated to be higher than the 20 year mean monthly value. During 3 days of light wind commercial bottom trawl operations were possible. Shipboard estimates of chlorophyll content in surface waters during trawling show the high concentrations that are indicative of a rich biomass of phytoplankton, a result of the upwelling episode. Satellite imagery shows the extent of the upwelling water to be of the order of 100 km offshore; the result of many upwelling episodes. Shipboard echo sounder data show the presence of various delmersal species and of zooplakton; the latter graze on the phytoplankton in the upper euphotic layers. The fish catch data are recorded according to species for 2 days of trawling, and the catch per trawl hour is recorded.
The results of global measurements of atmospheric water vapor by the Seasat Scanning Multichannel Microwave Radiometer and wave height and wind speed by the Seasat altimeter (ALT) are reported. The 13.5 GHz ALT has a 3.125 ns pulsewidth and 1022 Hz repetition rate, and measures surface height to a resolution exceeding 10 cm celative to a reference ellipsoid. Full ALT data comprise 135 km equatorial groundtracks, with about a 50 cm difference of sea wave height compared to buoy reference measurements, and windspeed accuracy to within 0.25-1.58 m/sec up to 20 m/sec. Highest water vapor concentrations were observed in the tropics and the lowest at high latitudes. Wind speeds were highest for the north-east and south-east tradewinds in both the Atlantic and Pacific oceans. Average wave height is small in the summer North Hemisphere and the largest waves are in the winter Southern ocean, and lowest in western Atlantic and Pacific ocean areas where winds are lightest.
The results of SAR, HF radar, wave rider buoy, and pressure sensor studies of wave behavior around San Clemente Island off the coast of California are reported. The SAR operated at a frequency of 1.2 GHz corresponding to a wavelength of 25 cm at 25 m resolution. Imagery was corrected for the slant range distortion and two-dimensional fast Fourier transforms were used to obtain two-dimensional wave number spectra. A 1 MW source was employed for the HF radar, with a receiving antenna synthesized by mounting the receiver on a van which drove along straight stretches of an oceanside highway. The measurement of 77 m waves displayed a shadow effect after the island, with an unexpected recovery which implies local wave generation. Reflected energy was determined to be too weak to account for the waves, and a nonlinear transfer of wave energy from waves moving parallel to the island was concluded to be the source of the observed inner wave energy.
During the 99 days of Seasat operation, two large-scale experiments were conducted which established the satellite sensors' wind measuring capabilities: (1) the Gulf of Alaska Experiment (GOASEX), and (2) the Joint Air Sea Interaction Experiment (JASIN), which unlike GOASEX was independent of the Seasat program and undertook comprehensive air and sea investigations which furnished excellent comparison data for Seasat. Qualitative comparison windfields were also provided by several storms. The point measurements in GOASEX and JASIN were averaged in conjunction with Seasat scatterometer regions and, on the basis of comparisons between several anemometers on buoys and meteorological ships and the calculation of various averaging times, a 20-min average yields a scatterometer scale windfield accuracy of up to + or 1 m/sec and + or - 10 deg in well-behaved windfields.
Seasat SASS fields for the North Atlantic were employed to test if meteorological features were discernible within the Seasat-produced wind fields, and if the features aided in determining a unique wind vector solution. Two groups were formed to work in isolation from each other until a true wind vector field was obtained for each SASS observation. The SASS data covered 1500 km swaths, and the angle of the Seasat antennas relative to the earth was known. Visible and IR data, along with surface weather stations, ship and ship buoy data were also available to the interpreters. Two-vector solutions by the two teams showed almost perfect agreement, and the alias problem was noted to reduce to a selection of two vectors 180 deg apart. Comparisons with the surface measurements in regards to wind directions resulted in agreement to within a standard deviation of 20% for direction. The SASS data is concluded to be useful for producing streamlines, isotachs, and mesoscale as well as cyclone-scale features.
The sensitivity of a Goddard Laboratory for Atmospheric Sciences global objective analysis cycle to the addition of FGGE level II-b data is assessed. The GOAS system comprises a predictive continuity provided by a model first-guess forecast integrated from a previous forecast and updated by data gathered in the interim. FGGE data originated in the Jan.-Mar. 1979 period and were acquired by rawinsondes, pilot balloons, surface stations, satellites, ships, and drifting buoys deployed during SOP-1. Focussing on 2-5 and 8-day forecasts, comparisons were made of the 6 hr forecast error at the 300 mb height in three experiments using all, no-satellite (NOSAT), and without rawinsondes or pilot balloons modes. Larger errors occurred in the case of NOSAT, while significant corrections to the GOAS predictions were noted using all the FGGE data. It was concluded that all forecasts were improved by inclusion of full FGGE data sets, including forecasting beyond one week.
An analysis is presented of the relative accuracy of Seasat scatterometer measurements of the wind speeds and directions at 19.5 m altitude as compared to ground truth measurements taken by surface ships and instrumented buoys. Attention is given to the JASIN, QE II, and GOASEX surface data. The validity of 2-30 min averages taken from surface stations spread out over a wide area and serving as a basis for defining wind field averages over the 50 km resolution of SASS is examined. Satisfactory wind speeds were found to be available from SASS readings in the wind speed range 6-14 m/sec. The use of 25 SASS readings around a grid point was determined to reduce scatter to 0.25 m/sec when used in numerical weather prediction modeling. Improvements to the SASS techniques by the Seasat successor, NOSS, are discussed, and inclusion of momentum, heat, and water turbulent fluxes by NOSS is noted.
The Scanning Multichannel Microwave Radiometer (SMMR), aboard both the SEASAT and Nimbus-7 satellites, was designed primarily to determine global sea surface temperatures and wind speeds over an extended range of atmospheric conditions. The Seasat mission lasted approximately three months from July to October 1978, during which time sufficient data was acquired to enable an assessment of SMMR measurement capabilities under a variety of conditions. This paper reports some results of initial Seasat SMMR assessments in the North Pacific area. A brief description is given of retrieval techniques used to derive the geophysical parameters. SMMR-derived sea surface temperatures and winds are compared with surface truth point measurements from XBT's and buoys, and with surface truth fields derived from point measurements. Accuracies of approximately 1.5 C and 2.5 m/s rms are obtained in these comparisons.
A microwave radar technique for remotely measuring the vector wave number spectrum of the ocean surface is described. The technique, which employs short-pulse, noncoherent radars in a conical scan mode near vertical incidence, is shown to be suitable for both aircraft and satellite application, the technique was validated at 10 km aircraft altitude, where we have found excellent agreement between buoy and radar-inferred absolute wave height spectra.