Engineering topics

Cavalieri, D. J.

Publications and source records attributed to Cavalieri, D. J..

At least 37 records · Page 2

NASA NTRS1988

Preliminary observations of polar sea ice with the Special Sensor Microwave Imager

The Special Sensor Microwave Imager (SSM/I) was launched as part of the Defense Meteorological Satellite Program. The SSM/I operates at 19.4, 22.2, 37.0, and 85.5 GHz with horizontal and vertical polarizations measured at each frequency except 22 GHz which has only a vertical polarization channel. Examination of polarization and spectral gradient ratios derived from the SSM/I radiances for open ocean, first-year, and multiyear Arctic sea ice reveals striking differences between the ratios calculated using lower frequencies and those ratios using the 85 GHz channels. These differences may serve as the basis for deriving sea ice information.

Cavalieri, D. J.↗

NASA NTRS1988

Arctic Sea ice studies with passive microwave satellite observations

The objectives of this research are: (1) to improve sea ice concentration determinations from passive microwave space observations; (2) to study the role of Arctic polynyas in the production of sea ice and the associated salinization of Arctic shelf water; and (3) to study large scale sea ice variability in the polar oceans. The strategy is to analyze existing data sets and data acquired from both the DMSP SSM/I and recently completed aircraft underflights. Special attention will be given the high resolution 85.5 GHz SSM/I channels for application to thin ice algorithms and processes studies. Analysis of aircraft and satellite data sets is expected to provide a basis for determining the potential of the SSM/I high frequency channels for improving sea ice algorithms and for investigating oceanic processes. Improved sea ice algorithms will aid the study of Arctic coastal polynyas which in turn will provide a better understanding of the role of these polynyas in maintaining the Arctic watermass structure. Analysis of satellite and archived meteorological data sets will provide improved estimates of annual, seasonal and shorter-term sea ice variability.

Cavalieri, D. J.↗

NASA NTRS1987

Multisensor comparison of ice concentration estimates in the marginal ice zone

Aircraft remote sensing data collected during the 1984 summer Marginal Ice Zone Experiment in the Fram Strait are used to compare ice concentration estimates derived from synthetic aperture radar (SAR) imagery, passive microwave imagery at several frequencies, aerial photography, and spectral photometer data. The comparison is carried out not only to evaluate SAR performance against more established techniques but also to investigate how ice surface conditions, imaging geometry, and choice of algorithm parameters affect estimates made by each sensor.Active and passive microwave sensor estimates of ice concentration derived using similar algorithms show an rms difference of 13 percent. Agreement between each microwave sensor and near-simultaneous aerial photography is approximately the same (14 percent). The availability of high-resolution microwave imagery makes it possible to ascribe the discrepancies in the concentration estimates to variations in ice surface signatures in the scene.

Burns, B. A.↗

NASA NTRS1987

On the relationship between atmospheric circulation and the fluctuations in the sea ice extents of the Bering and Okhotsk Seas

The influence of the hemispheric atmospheric circulation on the sea ice covers of the Bering Sea and the Sea of Okhotsk is examined using data obtained with the Nimbus 5 electrically scanning microwave radiometer for the four winters of the 1973-1976 period. The 3-day averaged sea ice extent data were used to establish periods for which there is an out-of-phase relationship between fluctuations of the two ice covers. A comparison of the sea-level atmospheric pressure field with the seasonal, interannual, and short-term sea ice fluctuations reveal an association between changes in the phase and the amplitude of the long waves in the atmosphere and advance and retreat of Arctic ice covers.

Cavalieri, D. J.↗

NASA NTRS1986

Active/passive microwave sensor comparison of MIZ-ice concentration estimates

Active and passive microwave data collected during the 1984 summer Marginal Ice Zone Experiment in the Fram Strait (MIZEX 84) are used to compare ice concentration estimates derived from synthetic aperture radar (SAR) data to those obtained from passive microwave imagery at several frequencies. The comparison is carried out to evaluate SAR performance against the more established passive microwave technique, and to investigate discrepancies in terms of how ice surface conditions, imaging geometry, and choice of algorithm parameters affect each sensor. Active and passive estimates of ice concentration agree on average to within 12%. Estimates from the multichannel passive microwave data show best agreement with the SAR estimates because the multichannel algorithm effectively accounts for the range in ice floe brightness temperatures observed in the MIZ.

Burns, B. A.↗

NASA NTRS1986

Aircraft and satellite passive microwave observations of the Bering Sea ice cover during MIZEX West

Passive microwave measurements of the Bering Sea were made with the NASA CV-990 airborne laboratory during February. Microwave data were obtained with imaging and dual-polarized, fixed-beam radiometers in a range of frequencies from 10 to 183 GHz. The high resolution imagery at 92 GHz provides a particularly good description of the marginal ice zone delineating regions of open water, ice compactness, and ice-edge structure. Analysis of the fixed-beam data shows that spectral differences increase with a decrease in ice thickness. Polarization at 18 and 37 GHz distinguishes among new, young, and first-year ice types.

Cavalieri, D. J.↗

NASA NTRS1985

Satellite observations of sea ice

An overview is presented of Antarctic and Arctic sea ice studies using data from the Nimbus-5 ESMR and the Nimbus-7 SMMR passive microwave radiometers. Four years (1973-1976) of ESMR data for the Antarctic Ocean define the characteristics of the seasonal cycle including regional contrasts and interannual variations. Major advances include the discovery of the Weddell polynya and the presence of substantial areas of open water in the Antarctic winter pack ice. Regional differences in sea ice extent on time-scales of about a month are shown to be associated with variations in surface-wind fields. In the Arctic, the computation of sea ice concentration is complicated by the presence of multiyear ice, but the amount of multiyear ice becomes an important measurable quantity with dual-polarized, multifrequency passive microwave sensors. Analysis of SMMR data demonstrates its advantage for studying the spatial and temporal variability of the Arctic ice cover. Large observed interannual variations in the distribution of the multiyear pack ice and the presence of significant divergent areas in the central Arctic during winter contrast markedly with the classical view of the Arctic pack ice.

Cavalieri, D. J.↗

NASA NTRS1985

Observations of the polar regions from satellites using active and passive microwave techniques

Observations of the ocean ice, ice sheets, ice edges, and ocean waves in the Antarctic, performed by the Seasat and Nimbus-7 satellites are described. Specific features of the Seasat altimeter, the SAR, the Seasat-A Scatterometer System, and the Scanning Multichannel Microwave Radiometer (SMMR) are discussed, together with the advantages and limitations of each instrument as applied to the study of ice dynamics. The Nimbus-7 SMMR algorithm for calculating sea-ice concentrations is presented. In addition, the Seasat altimeter-derived data on wind speed and wave heights in the Southern Ocean, and on the ice sheets of the Antarctica and Greenland were evaluated.

Swift, C. T.↗

NASA NTRS1984

Passive microwave characteristics of the Bering Sea ice cover during Marginal Ice Zone Experiment (MIZEX) West

Cavalieri, D. J.↗

NASA NTRS1984

A summary of results from the first Nimbus 7 SMMR observations

Selected data obtained during the first year of operation of the scanning multichannel microwave radiometer (SMMR) on board the Nimbus 7 satellite (launched in late October 1978) have been used to calculate, on a global basis, various geophysical parameters over open oceans, polar regions, and terrain. Over open oceans these calculations have provided values for sea surface temperatures, near-surface winds, atmospheric water vapor in a column, and rainfall rates. In polar regions, sea ice concentration, multiyear ice fraction, and radiating temperatures have been obtained. Finally, the extent and water equivalence of snow cover over terrain have been calculated. These parameters have been compared with in situ measurements of the same geophysical parameters, where available, and the results of these comparisons are described. The self-consistency of the global displays of all the parameters is discussed along with the plans for archiving them for subsequent research purposes. A description of the SMMR calibration and data processing scheme is also given.

Gloersen, P.↗

NASA NTRS1984

Determination of sea ice parameters with the Nimbus 7 SMMR

A method of determining sea ice parameters using Nimbus 7 polarized multispectral radiance data obtained with the Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) is presented. Observed radiances from selected areas in the Arctic region for the period February 3-7, 1979 were used in computing algorithm coefficients. Polar maps of sea ice concentration, multiyear fraction, and ice temperature are illustrated for this period. The variation of the mean and standard deviation of ice concentration and multiyear ice fraction for a region of perennial ice cover over the first 11 months of SMMR operation is also presented. Comparisons are made between the calculated sea ice parameters and information obtained from previous studies using aircraft, submarine and surface observations. The absolute accuracy of the SMMR parameters remains uncertain.

Cavalieri, D. J.↗

NASA NTRS1983

MIZEX-WEST NASA CV-990 flight report

As part of the Bering Sea marginal ice zone winter experiment (MIZEX-WEST), the CV-990 airborne laboratory was flown to assess the potential of using an extended range of wavelengths for improving passive microwave sea ice observations from spacecraft and second to provide an overview of the MIZ for large-scale processes studies. The aircraft was equipped with both imaging and fixed-beam, dual-polarized passive microwave radiometers ranging from 1.5 millimeter to 3 centimeter wavelengths. Visual, photographic, and thermal (10.7 micron) infrared surface observations were also made from the aircraft to complement the microwave measurements. The flight operations and in-flight observations are discussed and each flight is summarized including flight objective and instrument status. Preliminary mosaic images obtained with the ESMR imager, Nimbus-7 orbits over the Bering Sea, ice observations obtained by an ice observer on board, and composite maps of the general ice conditions for the month of February are also presented.

Cavalieri, D. J.↗

NASA NTRS1983

Nimbus 7 SMMR observations of the Bering Sea ice cover during March 1979

Sea ice concentration contour maps derived from the 0.81 cm wavelength channels on the Nimbus 7 scanning multichannel microwave radiometer (SMMR) are compared with surface and aircraft data and with sea ice charts derived from the TIROS-N satellite imagery. The regional ice and weather data and the derivation of the TIROS ice charts are discussed, and the Nimbus 7 SMMR data and the physical basis of the algorithm used to retrieve ice concentrations are described. A detailed comparison of the SMMR imagery with all available surface, satellite, and meteorological data for two days in March, 1979 is made. The results show that the ice concentration maps derived from the 0.81 cm wavelength SMMR radiances provide accurate information on both the ice edge position and the location of low and high ice concentration regions within the Bering Sea pack ice.

Cavalieri, D. J.↗

NASA NTRS1983

Performance of an airborne imaging 92/183 GHz radiometer during the Bering Sea Marginal Ice Zone Experiment (MIZEX-WEST)

An airborne imaging 92/183 GHz radiometer was recently flown onboard NASA's Convair 990 research aircraft during the February 1983 Bering Sea Marginal Ice Zone Experiment (MIZEX-WEST). The 92 GHz portion of the radiometer was used to gather ice signature data and to generate real-time millimeter wave images of the marginal ice zone. Dry atmospheric conditions in the Arctic resulted in good surface ice signature data for the 183 GHz double sideband (DSB) channel situated + or - 8.75 GHz away from the water vapor absorption line. The radiometer's beam scanner imaged the marginal ice zone over a + or - 45 degrees swath angle about the aircraft nadir position. The aircraft altitude was 30,000 feet (9.20 km) maximum and 3,000 feet (0.92 km) minimum during the various data runs. Calculations of the minimum detectable target (ice) size for the radiometer as a function of aircraft altitude were performed. In addition, the change in the atmospheric attenuation at 92 GHz under varying weather conditions was incorporated into the target size calculations. A radiometric image of surface ice at 92 GHz in the marginal ice zone is included.

Gagliano, J. A.↗

NASA NTRS1982

The Bering Sea ice cover during March 1979: Comparison of surface and satellite data with the Nimbus-7 SMMR

During March 1979, field operations were carried out in the Marginal Ice Zone (MIZ) of the Bering Sea. The field measurements which included oceanographic, meteorological and sea ice observations were made nearly coincident with a number of Nimbus-7 and Tiros-N satellite observations. The results of a comparison between surface and aircraft observations, and images from the Tiros-N satellite, with ice concentrations derived from the microwave radiances of the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) are given. Following a brief discussion of the field operations, including a summary of the meteorological conditions during the experiment, the satellite data is described with emphasis on the Nimbus-7 SMMR and the physical basis of the algorithm used to retrieve ice concentrations.

Martin, S.↗

NASA NTRS1981

Large-scale variations in observed Antarctic Sea ice extent and associated atmospheric circulation

The 1974 Antarctic large scale sea ice extent is studied from data from Nimbus 2 and 5 and temperature and sea level pressure fields from the Australian Meteorological Data Set. Electrically Scanning Microwave Radiometer data were three-day averaged and compared with 1000 mbar atmospheric pressure and sea level pressure data, also in three-day averages. Each three-day period was subjected to a Fourier analysis and included the mean latitude of the ice extent and the phases and percent variances in terms of the first six Fourier harmonics. Centers of low pressure were found to be generally east of regions which displayed rapid ice growth, and winds acted to extend the ice equatorward. An atmospheric response was also noted as caused by the changing ice cover.

Cavalieri, D. J.↗

NASA NTRS1981

Nimbus-7 scanning multichannel microwave radiometer /SMMR/ in-orbit performance appraisal

Calibration and processing techniques enacted during first year of operation of the Nimbus-7 scanning multichannel microwave radiometer (SMMR) are described. It was found that in-orbit calibration was necessary, as was fine-tuning of the geophysical parameter retrieval parameters to account for anomalies such as lower-than-expected polarization differences in ocean radiances. Phase shifts in the scan angles were corrected in order to avoid polarization mixing. Calibration constants to eliminate cross-talk and phase shift effects were established for radiation reflected from the earth, then averaged over data from 300 orbits to fit points on a sine curve to better than 0.2 K accuracy. An iterative approach was determined to be necessary due to signal anomalies caused by antenna dish oscillations. Global ocean and atmosphere parameters used to construct a radiation model of ten latitude bands are presented for use in radiation transfer equations.

Gloersen, P.↗

NASA NTRS1981

Observation of sea ice properties with the Nimbus-7 SMMR

Techniques for treating Nimbus-7 scanning multispectral microwave radiometer (SMMR) data to retrieve information on sea ice parameters are discussed. The SMMR produces information on ice concentration, temperature, multiyear ice fraction, thin ice fraction, difference between thin and thick ice temperatures, and atmospheric opacity. Sea ice emissivities as determined from ground truth and Nimbus-7 SMMR observations are provided, noting the necessity to further characterize the values with a larger data base. It was found that longest wavelengths displayed the largest contrast between open water and sea. Ice emissivity polarization differences are no more than 0.15 at any wavelength, while water polarizations are never less than 0.52. Ice emissivity increases directly with wavelength, and water emissivity increases inversely. Algorithmic representations of SMMR data to retrieve sea ice parameters are described.

Cavalieri, D. J.↗