Engineering topics

Kahn, Ralph

Publications and source records attributed to Kahn, Ralph.

65 records · Page 4

NASA NTRS1992

Observations of Mars using Hubble Space Telescope

The lack of a continuous record of Martian meteorology or of volatile cycles on Mars for extended periods of several Martian years seriously hinders efforts to understand the physics of the Martian atmosphere and surface system. The spacecraft observations are limited to only a few isolated time periods, and the Earth based record is limited by the relatively short periods surrounding oppositions when telescopic observations can yield useful data. To remedy this situation, the authors have embarked on a three year program of Mars observations using the Hubble Space Telescope (HST). Several scientific investigations are being carried out using the images, including: a study of the albedo variations; unit mapping of spectral reflectances; determination of optical depths due to aerosols and condensates; a study of the properties of condensate clouds and hoods; comparison of surface and atmospheric features; observation of size and shape of the polar caps; and investigation of surface atmospheric phenomena.

James, Philip B.↗

NASA NTRS1992

Validating a large geophysical data set: Experiences with satellite-derived cloud parameters

We are validating the global cloud parameters derived from the satellite-borne HIRS2 and MSU atmospheric sounding instrument measurements, and are using the analysis of these data as one prototype for studying large geophysical data sets in general. The HIRS2/MSU data set contains a total of 40 physical parameters, filling 25 MB/day; raw HIRS2/MSU data are available for a period exceeding 10 years. Validation involves developing a quantitative sense for the physical meaning of the derived parameters over the range of environmental conditions sampled. This is accomplished by comparing the spatial and temporal distributions of the derived quantities with similar measurements made using other techniques, and with model results. The data handling needed for this work is possible only with the help of a suite of interactive graphical and numerical analysis tools. Level 3 (gridded) data is the common form in which large data sets of this type are distributed for scientific analysis. We find that Level 3 data is inadequate for the data comparisons required for validation. Level 2 data (individual measurements in geophysical units) is needed. A sampling problem arises when individual measurements, which are not uniformly distributed in space or time, are used for the comparisons. Standard 'interpolation' methods involve fitting the measurements for each data set to surfaces, which are then compared. We are experimenting with formal criteria for selecting geographical regions, based upon the spatial frequency and variability of measurements, that allow us to quantify the uncertainty due to sampling. As part of this project, we are also dealing with ways to keep track of constraints placed on the output by assumptions made in the computer code. The need to work with Level 2 data introduces a number of other data handling issues, such as accessing data files across machine types, meeting large data storage requirements, accessing other validated data sets, processing speed and throughput for interactive graphical work, and problems relating to graphical interfaces.

Kahn, Ralph↗

NASA NTRS1992

Experience of the JPL Exploratory Data Analysis Team at validating HIRS2/MSU cloud parameters

Validation of the HIRS2/MSU cloud parameters began with the cloud/climate feedback problem. The derived effective cloud amount is less sensitive to surface temperature for higher clouds. This occurs because as the cloud elevation increases, the difference between surface temperature and cloud temperature increases, so only a small change in cloud amount is needed to effect a large change in radiance at the detector. By validating the cloud parameters it is meant 'developing a quantitative sense for the physical meaning of the measured parameters', by: (1) identifying the assumptions involved in deriving parameters from the measured radiances, (2) testing the input data and derived parameters for statistical error, sensitivity, and internal consistency, and (3) comparing with similar parameters obtained from other sources using other techniques.

Kahn, Ralph↗

NASA NTRS1991

Validating a large geophysical data set - Experiences with satellite-derived cloud parameters

The goal of this study is to validate the global cloud parameters derived from the satellite-borne HIRS2 and MSU atmospheric sounding instrument measurements, and to use the analysis of these data as one prototype for studying large geophysical data sets in general. The HIRS2/MSU data set contains a total of 40 physical parameters, filling 25 MB/day; raw HIRS2/MSU data are available for a period exceeding 10 years. Validation involves developing a quantitative sense for the physical meaning of the derived parameters over the range of environmental conditions sampled. This is accomplished by comparing the spatial and temporal distributions of the derived quantities with similar measurements made using other techniques, and with model results. The need to work with Level 2 (point) data, rather than Level 3 (gridded) data for validation purposes is discussed, and some techniques developed for charting the assumptions made in deriving an algorithm and generating a code to produce geophysical quantities from measured radiances are presented.

Kahn, Ralph↗

NASA NTRS1991

Hubble Space Telescope observations of Mars

Hubble Space Telescope (HST) afforded the possibility of resolving features as small as 100 km on the Martian surface even when it is at the far point of its orbit. Therefore it is ideally suited for monitoring seasonal changes on the red planet. The objectives research include: the study of Martian dust storms; use of images obtained through different filters to study the spectral reflectance of regions on the Martian surface; use of ultraviolet images and spectra to measure the amount of ozone in the planet's atmosphere as a function of location of the planet; use of images to study changes in the albedo of the Mars surface; and use of Planetary Camera images to study Martian clouds and to measure the opacity of the atmosphere.

James, Philip B.↗

NASA NTRS1991

Planetary atmospheres

Data published between 1987 and 1990 on the compositions and properties of different planetary atmospheres are reviewed. The origins and the evolutions of atmospheres of the outer planets and of their moons are discussed, and the relationships among waves, axisymmetric circulation, and global-scale transports are examined. Particular attention is given to the features of thin atmospheres of Mercury, Io, Triton, Pluto, and the earth's moon.

Kahn, Ralph↗

NASA NTRS1990

Ice haze, snow, and the Mars water cycle

Light curves and extinction profiles derived from Martian limb observations are used to constrain the atmospheric temperature structure in regions of the atmosphere with thin haze and to analyze the haze particle properties and atmospheric eddy mixing. Temperature between 170 and 190 K are obtained for three cases at levels in the atmosphere ranging from 20 to 50 km. Eddy diffusion coefficients around 100,000 sq cm/s, typical of a nonconvecting atmosphere, are derived in the haze regions at times when the atmosphere is relatively clear of dust. This parameter apparently changes by more than three orders of magnitude with season and local conditions. The derived particle size parameter varies systematically by more than an order of magnitude with condensation level, in such a way that the characteristic fall time is always about one Martian day. Ice hazes provide a mechanism for scavenging water vapor in the thin Mars atmosphere and may play a key role in the seasonal cycle of water on Mars.

Kahn, Ralph↗

NASA NTRS1989

The crush of new earth science data knocking at our door

The reasons for collecting massive amounts of earth science data in the Earth Observing System (EOS) Project are discussed. A processing hierarchy for handling the data is described, and the prospects for adequate throughput and storage for operational data analysis in the EOS era are addressed. Needs for successful exploratory data analysis are examined, and the policy issues implicated by the large stream of EOS data are considered.

Kahn, Ralph↗

NASA NTRS1988

Coping with all the earth science data

A report on the NASA-sponsored Earth Science and Applications Data Systems (ESADS) Workshop is presented. The ESADS report is reviewed and the task groups of the workshop are listed. The program set up to implement the recommendations of the workshop is discussed. The priorities of the ESADS committee recommendations include the development of standards and guidelines for data and metadata exchange, the creation of interoperable catalogs and directories, the development of guidelines for ancillary data archives, development of standard user interfaces, providing greater bandwidth in the user environment, collecting information about data storage technologies, and providing improved network connectivity.

Kahn, Ralph↗

NASA NTRS1987

Integration of multi-discipline data processing for earth observing systems

The first steps taken to ensure the controlled evolution of existing facilities toward greater interoperability and sharing of resources among NASA-supported earth science and applications data systems (ESADS) are described. Recommendations made by the various panels during the 1987 ESADS Workshop are presented. The panels were concerned with directories and catalogs, data archives, data manipulation software, computational facilities, data storage media, database management, and networking. Consideration was also given to the tracking and tuning of overall development and management coordination issues.

Kahn, Ralph↗

NASA NTRS1986

The vertical structure of limb hazes in the Martian atmosphere

Vertical distribution and reflectance properties of aerosols in the Martian atmosphere are presented, based on Viking Orbiter images containing the planetary limb. Profiles of scattered light above the limb are used to constrain the temporal and spatial behavior of the aerosols. The data cover a wide range of seasons, locations, and viewing geometries. The typical atmospheric column contains one or more discrete, optically thin, ice-like haze layers between 30 and 90 km elevation, depending on the season, whose composition is inferred to be water ice. Below the detached hazes there is a continuous haze extending to the surface. The continuous haze is rarely above 50 km and is much redder in color than the detached hazes above, implying a composition that has a strong dust component. The aerosol distribution exhibits solid seasonal control inferred to be driven by the variable solar flux around the orbit of Mars.

Jaquin, Fred↗