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NASA NTRS2002

Progress on Passive Sensor for Ultra-Precise Measurement of Carbon Dioxide from Space

Global measurements of atmospheric carbon dioxides (CO2) are needed to resolve significant discrepancies that exist in our understanding of the global carbon budget and, therefore, man's role in global climate change. The science measurement requirements for CO2 are extremely demanding (precision c .3%) No atmospheric chemical species has ever been measured from space with this precision. We are developing a novel application of a Fabry-Perot interferometer to detect spectral absorption of reflected sunlight by CO2 and O2 in the atmosphere. Preliminary design studies indicate that the method will be able to achieve the sensitivity and signal-to-noise required to measure column CO2 at the target specification. We are presently engaged in the construction of a prototype instrument for deployment on an aircraft to test the instrument performance and our ability to retrieve the data in the real atmosphere. In the first 6 months we have assembled a laboratory bench system to begin testing the optical and electronic components. We are also undertaking some measurements of signal and noise levels for actual sunlight reflecting from the ground. We shall present results from some of these ground based studies and discuss their implications for a space based system.

Heaps, William S.↗

NASA NTRS1997

Vibrational force alters mRNA expression in osteoblasts

Serum-deprived mouse osteoblastic (MC3T3E1) cells were subjected to a vibrational force modeled by NASA to simulate a space shuttle launch (7.83 G rms). The mRNA levels for eight genes were investigated to determine the effect of vibrational force on mRNA expression. The mRNA levels of two growth-related protooncogenes, c-fos and c-myc, were up-regulated significantly within 30 min after vibration, whereas those of osteocalcin as well as transforming growth factor-beta1 were decreased significantly within 3 h after vibration. No changes were detected in the levels of beta-actin, histone H4, or cytoplasmic phospholipase A2 after vibration. No basal levels of cyclooxygenase-2 expression were detected. In addition, the extracellular concentrations of prostaglandin E2 (PGE2), a potent autocrine/paracrine growth factor in bone, were not significantly altered after vibration most likely due to the serum deprivation state of the osteoblasts. In comparison with the gravitational launch profile, vibrational-induced changes in gene expression were greater both in magnitude and number of genes activated. Taken together, these data suggest that the changes in mRNA expression are due to a direct mechanical effect of the vibrational force on the osteoblast cells and not to changes in the local PGE2 concentrations. The finding that launch forces induce gene expression is of utmost importance since many of the biological experiments do not dampen vibrational loads on experimental samples. This lack of dampening of vibrational forces may partially explain why 1-G onboard controls sometimes do not reflect 1-G ground controls. These data may also suggest that scientists use extra ground controls that are exposed to launch forces, have these forces dampened on launched samples, or use facilities such as Biorack that provide an onboard 1-G centrufuge in order to control for space shuttle launch forces.

NASA Discipline Cell Biology↗

NASA NTRS2005

Ionospheric Transmission Losses Associated with Mars-orbiting Radars

There are a number of obstacles to radar sounding of the deep Martian subsurface from orbit, including signal losses from the medium conductivity, layer reflective losses, and ground clutter. Another adverse process is signal loss as radio waves propagate through the ionospheric plasma medium. The ionosphere is a plasma consisting of free electrons, ions and neutrals that can effectively damp/attenuate radar signals via electrodneutral collisions. The effect is most severe for transmissions at lower frequencies, which, unfortunately, are also favorable transmissions for deep penetration into the subsurface.

Farrell, W. M.↗

NASA NTRS2003

Delay/Doppler-Mapping GPS-Reflection Remote-Sensing System

A radio receiver system that features enhanced capabilities for remote sensing by use of reflected Global Positioning System (GPS) signals has been developed. This system was designed primarily for ocean altimetry, but can also be used for scatterometry and bistatic synthetic-aperture radar imaging. Moreover, it could readily be adapted to utilize navigation-satellite systems other than the GPS, including the Russian Global Navigation Satellite System GLONASS) and the proposed European Galileo system. This remote-sensing system offers both advantages and disadvantages over traditional radar altimeters: One advantage of GPS-reflection systems is that they cost less because there is no need to transmit signals. Another advantage is that there are more simultaneous measurement opportunities - one for each GPS satellite in view. The primary disadvantage is that in comparison with radar signals, GPS signals are weaker, necessitating larger antennas and/or longer observations. This GPS-reflection remote-sensing system was tested in aircraft and made to record and process both (1) signals coming directly from GPS satellites by means of an upward-looking antenna and (2) GPS signals reflected from the ground by means of a downward-looking antenna. In addition to performing conventional GPS processing, the system records raw signals for postprocessing as required.

Lowe, Stephen↗

NASA NTRS2012

Airborne Measurements of Atmospheric Pressure made Using an IPDA Lidar Operating in the Oxygen A-Band

We report airborne measurements of atmospheric pressure made using an integrated path differential absorption (IPDA) lidar that operates in the oxygen A-band near 765 nm. Remote measurements of atmospheric temperature and pressure are needed for NASA s Active Sensing of CO2 Emissions Over Nights, Days, and Seasons (ASCENDS) mission to measure atmospheric CO2. Accurate measurements of tropospheric CO2 on a global scale are very important in order to better understand its sources and sinks and to improve our predictions of climate change. The goal of ASCENDS is to determine the CO2 dry mixing ratio with lidar measurements from space at a level of ~1 ppm. Analysis to date shows that with current weather models, measurements of both the CO2 column density and the column density of dry air are needed. Since O2 is a stable molecule that uniformly mixed in the atmosphere, measuring O2 absorption in the atmosphere can be used to infer the dry air density. We have developed an airborne (IPDA) lidar for Oxygen, with support from the NASA ESTO IIP program. Our lidar uses DFB-based seed laser diodes, a pulsed modulator, a fiber laser amplifier, and a non-linear crystal to generate wavelength tunable 765 nm laser pulses with a few uJ/pulse energy. The laser pulse rate is 10 KHz, and average transmitted laser power is ~20 mW. Our lidar steps laser pulses across a selected line O2 doublet near 764.7 nm in the Oxygen A-band. The direct detection lidar receiver uses a 20 cm diameter telescope, a Si APD detector in Geiger mode, and a multi-channel scalar to detect and record the time resolved laser backscatter in 40 separate wavelength channels. Subsequent analysis is used to estimate the transmission line shape of the doublet for the laser pulses reflected from the ground. Ground based data analysis allows averaging from 1 to 60 seconds to increase SNR in the transmission line shape of the doublet. Our retrieval algorithm fits the expected O2 lineshapes against the measurements and determines the atmospheric pressure by minimizing the error between the observations and model. We first demonstrated our airborne lidar during flights during summer 2010. We made several improvements and made measurements during the Ascends flights during July 2011. More information about the technique, lidar instrument, airborne measurements, and pressure estimates will be described in the presentation.

Riris, Haris↗

NASA NTRS2013

RF Exposure Analysis for Multiple Wi-Fi Devices In Enclosed Environment

Wi-Fi devices operated inside a metallic enclosure have been investigation in the recent years. A motivation for this study is to investigate wave propagation inside an enclosed environment such as elevator, car, aircraft, and spacecraft. There are performances and safety concerned that when the RF transmitters are used in the metallic enclosed environments. In this paper, the field distributions inside a confined room were investigated with multiple portable Wi-Fi devices. Computer simulations were performed using the rigorous computational electromagnetics (CEM). The method of moments (MoM) was used to model the mutual coupling among antennas. The geometrical theory of diffraction (GTD) was applied for the multiple reflections off the ground and walls. The prediction of the field distribution inside such environment is useful for the planning and deployment of a wireless radio and sensor system. Factors that affect the field strengths and distributions of radio waves in confined space were analyzed. The results could be used to evaluate the RF exposure safety in confined environment. By comparing the field distributions for various scenarios, it was observed that the Wi-Fi device counts, spacing and relative locations in the room are important factors in such environments. The RF Keep Out Zone (KOZ), where the electric field strengths exceed the permissible RF exposure limit, could be used to assess the RF human exposure compliance. As shown in this study, it s possible to maximize or minimize field intensity in specific area by arranging the Wi-Fi devices as a function of the relative location and spacing in a calculated manner.

Hwu, Shian U.↗

NASA NTRS2013

Analytic Theory of Titans Schumann Resonance: Constraints on Ionospheric Conductivity and Buried Water Ocean

This study presents an approximate model for the atypical Schumann resonance in Titan's atmosphere that accounts for the observations of electromagnetic waves and the measurements of atmospheric conductivity performed with the Huygens Atmospheric Structure and Permittivity, Wave and Altimetry (HASI-PWA) instrumentation during the descent of the Huygens Probe through Titan's atmosphere in January 2005. After many years of thorough analyses of the collected data, several arguments enable us to claim that the Extremely Low Frequency (ELF) wave observed at around 36 Hz displays all the characteristics of the second harmonic of a Schumann resonance. On Earth, this phenomenon is well known to be triggered by lightning activity. Given the lack of evidence of any thunderstorm activity on Titan, we proposed in early works a model based on an alternative powering mechanism involving the electric current sheets induced in Titan's ionosphere by the Saturn's magnetospheric plasma flow. The present study is a further step in improving the initial model and corroborating our preliminary assessments. We first develop an analytic theory of the guided modes that appear to be the most suitable for sustaining Schumann resonances in Titan's atmosphere. We then introduce the characteristics of the Huygens electric field measurements in the equations, in order to constrain the physical parameters of the resonating cavity. The latter is assumed to be made of different structures distributed between an upper boundary, presumably made of a succession of thin ionized layers of stratospheric aerosols spread up to 150 km and a lower quasi-perfect conductive surface hidden beneath the non-conductive ground. The inner reflecting boundary is proposed to be a buried water-ammonia ocean lying at a likely depth of 55-80 km below a dielectric icy crust. Such estimate is found to comply with models suggesting that the internal heat could be transferred upwards by thermal conduction of the crust, while convective processes cannot be ruled out.

TITAN↗

NASA NTRS1984

Bidirectional Spectral Reflectance of Earth Resources: Influence of Scene Complexity and Atmospheric Effects on Remote Sensing

Practical methods for remote sensing when scene complexity and atmospheric effects modify intrinsic reflective properties are developed. The radiation history from ground to space of light reflected from individual leaves is initially multiply scattered within the crop canopy, whose geometry provides a controlling influence, then scattered and attenuated as a result of transmission through the Earth's atmosphere. The experimental and theoretical tools for studying these effects quantitatively are under development. A new radiative transfer code which uses Fourier transforms to solve the 3-D equation of transfer was developed. The initial version permits inhomogeneous non-Lambertian surfaces but assumes horizontal uniformity for the atmosphere. The computational results are in excellent agreement with Monte Carlo calculations. Laboratory apparatus to study the variation of spectral reflectance of individual leaves as a function of illumination incidence angle and reflection angle was used. These data can then be used in models to determine canopy scattering effects. Stress tests by observing leaf reflectance at 0.9 microns as a function of time following clipping from the stem was performed. A reflectance increase due to loss of water has been observed.

Diner, D. J.↗

NASA NTRS1986

Use of SIR-A and Landsat MSS data in mapping shrub and intershrub vegetation at Koonamore, South Australia

Shrublands cover much of the interior of the Australian continent and support a large grazing industry. Distinguishing the woody perennial vegetation from the smaller herbaceous vegetation and soil-encrusting lichen found between the shrubs is critical for range management but is difficult to do using Landsat data alone. In this study Shuttle Imaging Radar-A (SIR-A) and Landsat data acquired over Koonamore Station are examined together. Given the low topography and fine textured soils at Koonamore, radar return should be primarily determined by the percent area occupied by shrubs. During periods when most of the vegetation was non-vigorous and spectrally homogeneous, SIR-A data, as a surrogate measure of shrub cover, allowed the reflectance due to shrubs in Landsat data to be separated from the reflectance due to the intervening ground. This method allows estimation of the intershrub reflectance properties that are related to herbaceous vegetation, lichen, and bare soil exposures.

Green, G. M.↗

NASA NTRS1989

The MSAT-X MARECS B2 satellite experiment - Ground segment results

The results of a recently completed satellite experiment employing the JPL MSAT-X developed land-mobile satellite communication terminal are described. In this experiment, a full duplex 4800-b/s digital data and voice communication link was established through the INMARSAT Marecs B2 satellite between Atlantic City, New Jersey, and Southbury, Connecticut. A series of experiments was performed to characterize the terminal performance over this link. The basic experimental setup and the preliminary results of the speech and data experiments are presented. The satellite environment proved to be near to what was expected, and as a result the experimental results were very close to theory/simulation/laboratory experiments. It was found that the ground-to-ground communication links were more benign links than the ground-to-air and air-to-ground links, and this is reflected in the improved margins for the ground-to-ground links (approximately 5 dB versus 3.2 dB for the aeronautical links).

Jedrey, Thomas C.↗

NASA NTRS1998

NASA Hitchhiker Program Customer Payload Requirements (CPR)

The mission objective is to demonstrate each of the three types of technology intended for future small-satellite communications system design. Each experiment in the overall package is designed to exercise a different technology objective that may be found in the overall satellite communications and telemetry system design. The data communications through TORSS portion is designed to demonstrate that low-power communications systems with non-gimbaled antenna systems can transport significant quantities of data through TDRSS to the ground based on only transmitting through a TDRS when the experiment is near the TDRS subsatellite point. The remaining time. the payload communications system is not active. The demand access experiment is to demonstrate that the request for a demand access service can be transmitted through TDRS and received and decoded at the ground station. In this mode, the TDRS does not track the experiment but signal processing components at the White Sands Complex are used to detect and track the transmitted request. The laser communications experiment is designed to demonstrate passive transmission of telemetry data from the experiment. This mode uses a ground-based laser source to illuminate the experiment and modulate the beam with the data. Ground-based reception recovers the data from the reflected beam back to the ground station.

Horan, Stephen↗

NASA NTRS2007

System Characterization Results for the QuickBird Sensor

An overall system characterization was performed on several DigitalGlobe' QuickBird image products by the NASA Applied Research & Technology Project Office (formerly the Applied Sciences Directorate) at the John C. Stennis Space Center. This system characterization incorporated geopositional accuracy assessments, a spatial resolution assessment, and a radiometric calibration assessment. Geopositional assessments of standard georeferenced multispectral products were obtained using an array of accurately surveyed geodetic targets evenly spaced throughout a scene. Geopositional accuracy was calculated in terms of circular error. Spatial resolution of QuickBird panchromatic imagery was characterized based on edge response measurements using edge targets and the tilted-edge technique. Relative edge response was estimated as a geometric mean of normalized edge response differences measured in two directions of image pixels at points distanced from the edge by -0.5 and 0.5 of ground sample distance. A reflectance-based vicarious calibration approach, based on ground-based measurements and radiative transfer calculations, was used to estimate at-sensor radiance. These values were compared to those measured by the sensor to determine the sensor's radiometric accuracy. All imagery analyzed was acquired between fall 2005 and spring 2006. These characterization results were compared to previous years' results to identify any temporal drifts or trends.

Holekamp, Kara↗

NASA NTRS1986

Radiation physics and modelling for off-nadir satellite-sensing of non-Lambertian surfaces

The primary objective of this paper is to provide a deeper understanding of the physics of satellite remote-sensing when off-nadir observations are considered. Emphasis is placed on the analysis and modeling of atmospheric effects and the radiative transfer of non-Lambertian surface reflectance characteristics from ground-level to satellite locations. The relative importance of spectral, spatial, angular, and temporal reflectance characteristics for satellite-sensed identification of vegetation types in the visible and near-infrared wavelength regions is evaluated. The highest identification value is attributed to angular reflectance signatures. Using radiative transfer calculations to evaluate the atmospheric effects on angular reflectance distributions of vegetation surfaces, atmosphere-invariant angular reflectance features such as the 'hot spot' and the 'persistent valley' are identified. A new atmospheric correction formalism for complete angular reflectance distributions is described. A sample calculation demonstrates that a highly non-Lambertian measured surface reflectance distribution can be retrieved from simulated satellite data in the visible and near infrared to within about 20 percent accuracy for almost all view directions up to 60 deg off-nadir. Thus the high value of angular surface reflectance characteristics (the 'angular signature') for satellite-sensed feature identification is confirmed, which provides a scientific basis for future off-nadir satellite observations.

Gerstl, S. A.↗

NASA NTRS2005

Evaluation of MISR Land Surface BRF Measurements: Intercomparison with Coincident Airborne and Ground Field Measurements

The bidirectional reflectance factor, BRF, retrieved by the Multiangle Imaging SpectroRadiometer, MISR, is compared with those coincidently measured from aircraft, by the Cloud Absorption Radiometer, CAR, and MISR airborne simulator, AirMISR, and on the ground, by the Portable Apparatus for Rabid Acquisition of Bidirectional Observations of Land and Atmosphere, PARABOLA Ill. The intercomparisons are made for six types of surfaces: bright desert, salt pans, grassland, forests, snow and the Dismal Swamp. The results show that MISR BRF values are mostly within +/- 10% in agreement with the corresponding airborne and ground measurements, independent of the surface types This study is part of an effort to evaluate and validate MISR surface products.

Multiangle Imaging SpectroRadiometer (MISR)↗

NASA NTRS1980

Characterization of reflected light from the space power system

Sunlight reflected off large space structures is examined. To assure that this illumination does not exceed the irradiance tolerances of the eye, reflections from these satellites must be controlled by vehicle orientation and surface specifications. The components of various space power system vehicles to determine the reflectances which will significantly contribute to the ground illumination are evaluated. Calculations of reflected solar intensity from various satellite system elements requires description of the elements and of the geometry potential reflectance paths. Surface intensity and the conditions under which it will illuminate a portion of the Earth are also determined.

Liemohn, H. B.↗

NASA NTRS1981

Ground ice on Mars - Inventory, distribution, and resulting landforms

A model is presented for the distribution of ground ice on Mars, and model predictions are compared with Viking Orbiter photographs of landforms possibly related to ground ice. Estimates of the amount of water originally outgassed on Mars and the amount of water presently on Mars are presented which show that approximately 90% of the estimated outgassed volume may be stored in the Martian subsurface as ground ice. The extent of the Martian cryosphere, the zone in which the temperature is below the freezing point of water and in which ground ice can exist, is examined, and it is shown that, in the presence of a protective surface layer approximately 10 m thick, ground ice may occur beneath the entire Martian surface. Observed features on the Martian surface considered most likely to reflect the presence of ground ice are discussed, including thermokarst-like pits and debris flows, and possibly polygonally patterned ground, curvilinear features and pingo-like mounds, and the geographic distributions of these features as seen in Viking photographs are examined. It is found that the possibly ice-related features are concentrated in the northern midlatitudes, the equatorial zone near Olympus Mons, and the Southern Hemisphere near the edge of the plains, indicating that subsurface ice may be present over the entire planet. The origin of the ice-related landforms is explained by a combination of volcanic heating and variations in insolation.

Rossbacher, L. A.↗

NASA NTRS1987

The unusual dust-scattering properties in the reflection nebula CED 201

Spectrophotometric data available from ground-based and IUE observations of the reflection nebula CED 201 and its illuminating star BD + 69.1231 deg are analyzed to deduce the most likely star-nebula geometry and the wavelength dependence of the scattering characteristics of the nebular grains. The dust albedo is found to decline from 0.72 at V to probably less than 0.2 at lambda less than 2000 A, explaining the unusual red color of this reflection nebula. The wavelength dependence of the optical depth and of the phase function asymmetry in the visible suggests the existence of a narrow size distribution of grains, skewed toward larger than normal particle sizes. CED 201 is one of two reflection nebulae with positive evidence for enhanced scattering in the long-wavelength wing of the 2175 A dust extinction feature, also pointing toward larger than average grains.

Witt, A. N.↗

NASA NTRS1989

Senegalese land surface change analysis and biophysical parameter estimation using NOAA AVHRR spectral data

Surface biophysical estimates were derived from analysis of NOAA Advanced Very High Spectral Resolution (AVHRR) spectral data of the Senegalese area of west Africa. The parameters derived were of solar albedo, spectral visible and near-infrared band reflectance, spectral vegetative index, and ground temperature. Wet and dry linked AVHRR scenes from 1981 through 1985 in Senegal were analyzed for a semi-wet southerly site near Tambacounda and a predominantly dry northerly site near Podor. Related problems were studied to convert satellite derived radiance to biophysical estimates of the land surface. Problems studied were associated with sensor miscalibration, atmospheric and aerosol spatial variability, surface anisotropy of reflected radiation, narrow satellite band reflectance to broad solar band conversion, and ground emissivity correction. The middle-infrared reflectance was approximated with a visible AVHRR reflectance for improving solar albedo estimates. In addition, the spectral composition of solar irradiance (direct and diffuse radiation) between major spectral regions (i.e., ultraviolet, visible, near-infrared, and middle-infrared) was found to be insensitive to changes in the clear sky atmospheric optical depth in the narrow band to solar band conversion procedure. Solar albedo derived estimates for both sites were not found to change markedly with significant antecedent precipitation events or correspondingly from increases in green leaf vegetation density. The bright soil/substrate contributed to a high albedo for the dry related scenes, whereas the high internal leaf reflectance in green vegetation canopies in the near-infrared contributed to high solar albedo for the wet related scenes. The relationship between solar albedo and ground temperature was poor, indicating the solar albedo has little control of the ground temperature. The normalized difference vegetation index (NDVI) and the derived visible reflectance were more sensitive to antecedent rainfall amounts and green vegetation changes than were near-infrared changes. The information in the NDVI related to green leaf density changes primarily was from the visible reflectance. The contribution of the near-infrared reflectance to explaining green vegetation is largely reduced when there is a bright substrate.

Vukovich, Fred M.↗