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NASA NTRS1993

Topographic mapping using radar interferometry - Processing techniques

In the summer of 1991 the NASA DC-8 airborne synthetic aperture radar (SAR) system acquired data with the radar configured in a C-band across-track interferometer mode. The data were processed to generate rectified topographic maps. A new processing scheme was developed featuring motion compensation, absolute phase retrieval, and three-dimensional 1ocation. The new processor has been tested using data which were acquired with extreme aircraft motion so that performance could be evaluated under adverse conditions. The topographic maps generated by the radar were compared to Digital Elevation Models (DEM's) derived using conventional optical stereo techniques. In one region we measured rms elevation deviations which were less than the specified DEM accuracy, and in the region covered by the more accurate DEM we found errors varying from 2.2 m rms in relatively flat terrain up to 5.0 m in mountainous areas. The rms difference between radar and DEM elevations over the 6.5 km by 22 km area covered by the more accurate DEM was 3.6 m.

Madsen, Soren N.↗
NASA NTRS1991

Infrared lidars for atmospheric remote sensing

Lidars using pulsed TEA-CO2 transmitters and coherent receivers have been developed at JPL and used to measure atmospheric backscatter and extinction at wavelengths in the 9-11 micron region. The global winds measurement application of coherent Doppler lidar requires intensive study of the global climatology of aerosol and cloud backscatter and extinction. An airborne lidar was recently flown on the NASA DC-8 research aircraft for operation during two Pacific circumnavigation missions. The instrument characteristics, as well as representative measurement results, are discussed.

Menzies, Robert T.↗
NASA NTRS1992

Water vapor profiling over ocean surface with 90 GHz and 183 GHz measurements under clear and cloudy conditions

Radiometric measurements at 90 GHz and three sideband frequencies near the peak water vapor absorption line of 183.3 GHz were made with the Advanced Microwave Moisture Sounder (AMMS) aboard the NASA DC-8 aircraft over some regions of the Pacific Ocean. These measurements were used to retrieve atmospheric water vapor profiles over ocean surface using the algorithm developed by Schaerer and Wilheit (1979). The algorithm incorporates a mechanism to estimate cloud liquid water when the estimated relative humidity is greater than 95 percent. The results are compared with estimated values from measurements taken by the Special Sensor Microwave/Imager (SSMI) and TIROS Operational Vertical Sounder (TOVS). The water vapor profiles estimated from AMMS are generally higher at low altitudes and lower at high altitudes than those from the TOVS measurements. Cloud liquid water is retrieved from both AMMS and SSM/I measurements over the same general regions. The retrieved water vapor profiles show more fluctuations in these regions. It is concluded that the AMMS with only four channels of measurements may not be able to retrieve both water vapor and cloud information with authority.

Wang, J. R.↗
NASA NTRS1992

Mapping sub-tropical vegetation using multi-frequency, multi-polarization SAR data

In 1990 the NASA/JPL airborne synthetic aperture radar DC-8 (Airsar) was flown over an area in northern Belize and the surrounding countries of Guatemala and Mexico. The three-frequency polarimetric radar signatures of a variety of natural areas have been extracted, and many have a unique radar signature. Scattering mechanisms which may explain these signatures and results of an image classification technique are presented.

Freeman, A.↗
NASA NTRS1992

Hydrometeor discrimination in melting layer using multiparameter airborne radar measurement

Results from a multiparameter airborne radar/radiometer experiment (the Typhoon experiment) are presented. The experiment was conducted in the western Pacific with the NASA DC-8 aircraft, in which a dual-wavelength at X-band and Ka-band and dual-polarization at X-band radar was installed. The signatures of dBZ(X), dBZ(Ka), LDR (linear depolarization ratio) at X-band and DZ=dBZ(X)-dBZ(Ka) are discussed for the data obtained in the penetration of the typhoon Flo. With emphasis on discrimination of hydrometeor particles, some statistical features of the brightband in stratiform rain are discussed.

Kumagai, H.↗
NASA NTRS1989

Ozone Hole Airborne Arctic Stratospheric Expedition (Pre-Flight)

The first segment of this video gives an overview of the Ozone Hole Airborne Arctic Stratospheric Expedition, an international effort using balloon payloads, ground based instruments, and airborne instruments to study ozone depletion and the hole in the ozone over Antarctica which occurs every spring. False color imagery taken from NASA's Nimbus 7 satellite which documents daily changes in ozone is also shown. The second segment of this video shows actual take-off and flight footage of the two aircraft used in the experiment: the DC-8 Flying Laboratory and the high flying ER-2.

Source record↗
NASA NTRS1990

Ground truth measurement for the analysis of airborne SAR data recorded over Oberpfaffenhofen, FRG, 1989

As a preliminary investigation to the joint multiparameter SIR-C/X-SAR shuttle experiment of NASA/JPL (USA), DLR (FRG), and PSN (Italy) which is scheduled for the year 1992 an airborne SAR campaign was conducted over Oberpfaffenhofen, FRG, in August 1989. Primarily this campaign was planned to test and verify equipment and algorithms developed at the DLR to calibrate multifrequency polarimetric SAR data. Oberpfaffenhofen is designated as one of the super test sites for the SIR-C/X-SAR experiment which will be imaged under all circumstances except severe mission errors. A super test site drives radar parameters and look directions and the recorded SAR data will be calibrated. In addition ancillary data will be available for the site. During the airborne STAR campaign conducted in the week of August 14th 1989 various sensor types were used to record remote sensing data over the calibration test site and its vicinity: the polarimetric DC-8 JPL-SAR (P-, L-, C-band), the DLR airborne SAR (C-, X-band), color infrared aerial photography (DLR), and the truck-mounted scatterometer (C- and X-band) of the Institute for Navigation, University of Stuttgart (INS). Because of this variety of different sensor types used and out of the fact that sufficiently large forested and agriculturally used areas were planned to be covered by these sensors, the interest of several German research groups involved in investigations concerning SAR land applications arose. The following groups carried out different ground-truth measurements: University of Bonn, Institute for plant cultivation (plant morphology and moisture content); University of Braunschweig, Institute for Geography (soil moisture and surface roughness); University of Freiburg, Institute for Geography (dielectric soil properties, landuse); and University of Munich, Institute for Geography (landuse inventory, plant, surface, and soil parameters). This paper presents the joint ground truth activities of the Institute for Geography, University of Munich, and the German Remote Sensing Data Center of the DLR.

Bayer, T.↗
NASA NTRS1990

Dutch X-band SLAR calibration

In August 1989 the NASA/JPL airborne P/L/C-band DC-8 SAR participated in several remote sensing campaigns in Europe. Amongst other test sites, data were obtained of the Flevopolder test site in the Netherlands on August the 16th. The Dutch X-band SLAR was flown on the same date and imaged parts of the same area as the SAR. To calibrate the two imaging radars a set of 33 calibration devices was deployed. 16 trihedrals were used to calibrate a part of the SLAR data. This short paper outlines the X-band SLAR characteristics, the experimental set-up and the calibration method used to calibrate the SLAR data. Finally some preliminary results are given.

Groot, J. S.↗
NASA NTRS1990

Synthetic aperture radar observations of the Greenland ice sheet

Results of preliminary analyses of aircraft polarimetric SAR data acquired over the Greenland Ice Sheet are presented. Data were collected in August 1989 by the Jet Propulsion Laboratory (JPL) multifrequency, polarimetric SAR using the NASA DC-8 aircraft over southern Greenland. Data of this kind are the first to be acquired over an ice sheet. They are complementary to the limited coverage provided by the SEASAT satellite SAR in 1978, and more recent aircraft X-band SAR image coverage. Frequency and polarization dependencies observed in the P-, L-, and C-band image products are attributed to large-scale variations in the snow and ice surface characteristics. At this time of year, during the ablation season, ice topography exerts a strong influence upon drainage and other hydrological features on the ice sheet surface. Systematic trends in backscatter strength observed across regions of changing snow facies are suggestive of a capability to map areas of snow wetness. Trends observed at C-band indicate that algorithms could possibly be developed which have the ability to delineate areas of significant melt.

Jezek, K.↗
NASA NTRS1990

Comparison of active and passive microwave signatures of Arctic sea ice

In March 1988, overlapping active and passive microwave instrument data were acquired over Arctic sea ice using the NASA DC-8 aircraft equipped with multifrequency, variable polarization SAR and radiometer. Flights were conducted as a series of coordinated underflights of the DMSP SSM/I satellite radiometer in order to validate ice products derived from the SSM/I radiances. Subsequent flights by an NRL P-3 aircraft enabled overlapping high-resolution, single frequency image data to be acquired over the same regions using a Ka-band scanning microwave radiometer. In this paper, techniques are discussed for the accurate coregistration of the three aircraft datasets. Precise coregistration to an accuracy of 100 m plus or minus 25 m has, for the first time, enabled the detailed comparison of temporally and spatially coincident active and passive airborne microwave datasets. Preliminary results from the intercomparisons indicate that the SAR has highly frequency- and polarization-dependent signatures, which at 5.3 GHz (C-band) show an extremely high correlation with the 37 GHz radiometric temperatures.

Drinkwater, M. R.↗
NASA NTRS1993

AIRSAR deployment in Australia, September 1993: Management and objectives

Past co-operation between the NASA Earth Science and Applications Division and the CSIRO and Australian university researchers has led to a number of mutually beneficial activities. These include the deployment of the C-130 aircraft with TIMS, AIS, and NS001 sensors in Australia in 1985; collaboration between scientists from the USA and Australia in soils research which has extended for the past decade; and in the development of imaging spectroscopy where DSIRO and NASA have worked closely together and regularly exchanged visiting scientists. In May this year TIMS was flown in eastern Australia on board a CSIRO-owned aircraft together with a CSIRO-designed CO2 laser spectrometer. The Science Investigation Team for the Shuttle Imaging Radar (SIRC-C) Program includes one Australian Principal Investigator and ten Australian co-investigators who will work on nine projects related to studying land and near-shore surfaces after the Shuttle flight scheduled for April 1994. This long-term continued joint collaboration was progressed further with the deployment of AIRSAR downunder in September 1993. During a five week period, the DC-8 aircraft flew in all Australian states and collected data from some 65 individual test sites.

Milne, A. K.↗
NASA NTRS1993

Atmospheric nuclei in the Pacific midtroposphere: Their nature, concentration, and evolution

An extensive flight series was carried out during May-June 1990 in the remote North and South Pacific free tropospheric aboard the NASA DC-8. Condensation nuclei counters and optical particle counters provided information on aerosol particles with diameters between 0.003 and 7.0 micrometers. Vertical profiles revealed aerosol layers to be a common feature of the free troposphere. Regions with highest aerosol mass tended to have the highest concentrations of surface-derived nuclei but the lowest concentrations of total nuclei. Regions with lowest aerosol mass tended to have the highest concentrations of the smaller 'ultrafine' condensation nuclei with diameters below 0.02 mircometers. Horizontal transects totaling over 35,000 km at about 9 to 10-km altitude exhibited variability of approximately 3 orders of magnitude in both aerosol mass and number concentrations over spatial scales ranging from 1 to 1000 km. At these altitudes an approximate inverse relationship between ultrafine concentrations and the surface area of the larger aerosol was evident. Regions having lowest aerosol mass were characterized by aerosol thermal volatility, indicative of a predominately sulfuric acid composition, and by very high concentrations of ultrafine nuclei, indicative of recent homogeneous nucleation. These conditions were frequently observed but were conspicuously evident above cloud over the intertropical convergence zone. The clean, free troposphere appears to be a significant source region for new tropospheric nuclei. A simplified model of the lifetime, coagulation, and cycling of these nuclei suggests that they constitute a source of cloud condensation nuclei in the lower troposphere.

Clarke, Antony D.↗
NASA NTRS1993

Airborne Arctic Stratospheric Expedition 2: An overview

The sudden onset of ozone depletion in the antarctic vortex set a precedent for both the time scale and the severity of global change. The Airborne Antarctic Ozone Experiment (AAOE), stages from Punta Arenas, Chile, in 1987, established that CFCs, halons, and methyl bromide, the dominant sources of chlorine and bromide radicals in the stratosphere, control the rate of ozone destruction over the Antarctic; that the vortex is depleted in reactive nitrogen and water vapor; and that diabatic cooling during the antarctic winter leads to subsidence within the vortex core, importing air from higher altitudes and lower latitudes. This last conclusion is based on observed dramatic distortion in the tracer fields, most notably N2O. In 1989, the first Airborne Arctic Stratospheric Expedition (AASE-1), staged from Stavanger, Norway, and using the same aircraft employed for AAOE (the NASA ER-2 and the NASA DC-8), discovered that while NO(x) and to some degree NO(y) were perturbed within the arctic vortex, there was little evidence for desiccation. Under these (in contrast to the antarctic) marginally perturbed conditions, however, ClO was found to be dramatically enhanced such that a large fraction of the available (inorganic) chlorine resided in the form of ClO and its dimer ClOOCl. This leaves two abiding issues for the northern hemisphere and the mission of the second Airborne Arctic Stratospheric Expedition (AASE-2): (1) Will significant ozone erosion occur within the arctic vortex in the next ten years as chlorine loading in the stratosphere exceeds four parts per billion by volume? (2) Which mechanisms are responsible for the observed ozone erosion poleward of 30 deg N in the winter/spring northern hemisphere reported in satellite observations?

Anderson, James G.↗
NASA NTRS1993

Airborne observations of the composition of the 1992 tropical stratosphere by FTIR solar absorption spectrometry

Vertical column measurements of the gaseous composition of the tropical stratosphere were made from the NASA DC-8 aircraft early in 1992. As anticipated, the burdens of the stratospheric source gases (e.g., O3, HF, HCl, ClNO3, HNO3) were reduced from their mid-latitude values due to increased uplift and photolysis. The tracers revealed considerably more uplift near the equator than the sub-tropics. For example, the HF burdens at +/- 20 deg latitude were nearly double those at 5 deg N. This, together with results obtained from other long-lived gases (e.g. N2O, CH4, CF2Cl2) indicates that volume mixing ratios found at 22 km altitude at mid-latitudes occurred at 26 km in the sub-tropics and at 30 km in the equatorial zone. This zone of uplift was symmetrical about the equator even though the sun was overhead at 20 deg S.

Toon, G. C.↗
NASA NTRS1993

Airborne brightness temperature measurements of the polar winter troposphere as part of the Airborne Arctic Stratosphere Experiment 2 and the effect of brightness temperature variations on the diabatic heating in the lower stratosphere

In this paper we report radiometric measurements of tropospheric brightness temperatures obtained during the AASE 2 experiment. These measurements represent the first attempt to characterize effective radiative temperatures as seen from above the troposphere during the Arctic winter. The reported measurements include brightness temperatures at 6.7 and 10.5 microns as seen from the NASA DC-8 aircraft flying at about 11 km altitude. We also present radiative transfer calculations to estimate the effect of tropospheric brightness temperature on the lower stratospheric heating rates. Because of the recent massive eruption of the Pinatubo volcano, we also discuss the effects of a volcanic aerosol layer. It is concluded that small particles like the volcanic aerosol or polar stratospheric clouds (PSCs) type 1 do not affect stratospheric heating rates by much; on the other hand, larger particles, PSCs types 2 and 3, may have significant effects on heating rates and consequently on dynamics of the lower stratosphere. The dynamical effects of local stratospheric temperature variations are briefly discussed.

Valero, Francisco P. J.↗
NASA NTRS1993

Observations of Upper Atmospheric Optical Flashes Recorded From an Aircraft

Short-duration upper atmospheric optical flashes were recorded on the night of 8 July, 1993 (9 July UT) from the NASA DC-8 Airborne Laboratory flying over the American Midwest. All-sky video images from an intensified silicon intensified target (ISIT) camera revealed 19 upper atmospheric flashes occurring over a period of approximately 100 min. The flashes were similar in appearance to previously reported ground and shuttle-based video observations. Detailed analysis of 12 of the events yielded these parameters: (1) duration less than or = 17 ms; (2) brightness 10-50 kR, roughly that of bright aurorae; (3) terminal heights 30-100 km, with a mean of approximately 60 km; (4) horizontal extent 10-50 km; and (5) emission volume greater than 1000 km(sup 3). The relative frequency of the optical flashes was (6) 1:200-1:400 compared to negative cloud-to-ground discharges and 1:20-1:40 compared to positive cloud-to-ground discharges.

Sentman, D. D.↗
NASA NTRS1993

Post-Pinatubo Optical Depth Spectra VS. Latitude and Vortex Structure: Airborne Tracking Sunphotometer Measurements in AASE 2

In January and March 1992, DC-8-measured stratospheric particle optical depth spectra, (tau)(sub p)(lambda), peaked broadly at midvisible or longer wavelengths. At mid-to-high northern latitudes outside the vortex, tau(sub p)(526 microns) above about 11 km was as large as 0.22 in both January and March, reflecting continued Pinatubo volcanic influence. In both months, in-vortex tau(sub p) above 11 km was smaller than outside-vortex values by a factor of two or more, and in January a strong anticorrelation was observed between tau(sub p)(lambda) and HF column content (an indicator of vortex penetration). In late January at 18-20S, near the edge of the southern subtropical jet, tau(sub p)(526 microns) above 12 km was only about 0.07- 0.09, with a flatter spectral shape than northern mid-to high-latitude measurements in both January and March. Occasional high-latitude vertical profiles indicate 6-1 km slab optical depths, delta(tau)(sub p)(526 micron), of 0.05 to 0.1, which should be added to the above-11-km values to yield values above 6 km.

Russell, P. B.↗
NASA NTRS1993

Airborne Brightness Temperature Measurements of the Polar Winter Troposphere as Part of the Airborne Arctic Stratosphere Experiment 2 and the Effect of Brightness Temperature Variations on the Diabatic Heating in the Lower Stratosphere

In this paper we report radiometric measurements of tropospheric brightness temperatures obtained during the AASE 2 experiment. These measurements represent the first attempt to characterize effective radiative temperatures as seen from above the troposphere during the Arctic winter. The reported measurements include brightness temperatures at 6.7 and 10.5 micrometers as seen from the NASA DC-8 aircraft flying at about 11 km altitude. We also present radiative transfer calculations to estimate the effect of tropospheric brightness temperature on the lower stratospheric heating rates. Because of the recent massive eruption of the Pinatubo volcano, we also discuss the effects of a volcanic aerosol layer. It is concluded that small particles like the volcanic aerosol or PSCs type 1 do not affect stratospheric heating rates by much; on the other hand, larger particles, PSCs types 2 and 3, may have significant effects on heating rates and consequently on dynamics of the lower stratosphere. The dynamical effects of local stratospheric temperature variations are briefly discussed.

Valero, Francisoco P. J.↗