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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.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Pinatubo Global- to Micro-Scale Evolution: A Unified Picture from Space, Air, and Ground Measurements

We combine space, air, and ground measurements to develop a composite picture of the post-Pinatubo aerosol, and assess the consistency and uncertainties of various measurement and retrieval techniques. impactor and optical counter measurements, as well as retrievals from optical depth spectra, paint a generally consistent picture of the evolution of particle effective radii, R(sub eff). In the first month after the eruption, although particle numbers increased by orders of magnitude, R(sub eff) was similar to the preeruption value of 4.2 micrometers, because both small (r less than 0.25 micrometers) and large (r greater than 0.6 micrometers) particles increased in number, Over the next 3-6 months, R(sub eff) increased rapidly to about 0.5 micrometers. In general, R(sub eff) continued to increase for about a year after the eruption. The peak wavelength of optical depth spectra increased from initial values of less than 0.42 micrometers to values between 0.78 and 1 micrometer. This coupled evolution in particle size distribution and optical depth spectra helps explain the relationship between the global maps of 0.5 and 1.0-micrometer optical depth derived from the AVHRR and SAGE satellite measurements. It also sets a context for evaluating remaining uncertainties in each of these satellite data products. We also make consensus recommendations for particle composition, shape, and temperature- and wavelength-dependent refractive index, and show how the latter effect on backscatter spectra can influence particle sizes retrieved from multiwavelength lidar measurements.

Russell, Philip B.↗
NASA NTRS1995

Pinatubo Aerosol Global-to-Micro-Scale Evolution: A Unified Picture From Space, Air, and Ground Measurements

We combine a variety of measurements to develop a composite picture of the post-Pinatubo aerosol and assess the consistency and uncertainties of the measurement and retrieval techniques Satellite infrared spectroscopy, particle morphology, and evaporation temperature measurements are in accord with theoretical calculations In showing a dominant particle composition of H2SO4-H2O mature with H2SO4 weight traction of 65-80% for most stratospheric temperatures and humidities. Important exceptions are: (1) the presence of volcanic ash at all attitudes initially and in a layer just above the tropopause until at least March 1992, and (2) much smaller H2SO4 weight fractions at the low temperatures attained In high latitude winters and at the tropical tropopause. Laboratory spectroscopy and theoretical calculations yield wavelength- and temperature-dependent refractive indices for the dominant H2SO4-H2O droplets. These in turn permit derivation of particle size spectra from measured optical depth spectra for comparison to direct measurements by impactors and optical counters, All three techniques paint a generally consistent picture of the evolution of R(sub eff) the effective, or area-weighted, particle radius. In the first month after the eruption, although particle numbers increased by orders of magnitude, R(sub eff) was similar to the pre-eruption value of 0.1 to 0.2 microns because both small (r less than 0.2 microns) and large (r greater than 0.6 microns) particles increased in number. Over the next 3-6 months, R(sub eff) increased to about 0.5 microns, reflecting particle growth through condensation and coagulation. In general, R(sub eff) continued to increase for about a year after the eruption. Extinction spectra computed from in situ size distribution measurements are consistent with optical depth measurements, which show spectra with maxima initially at wavelengths of 0.42 microns or less, and thereafter progressively increasing to between 0.78 and 1 micron. Not until 1993 does optical depth spectra begin to show a clear return to the preeruption signature of maximizing at the shortest visible wavelengths or in the near UV. This coupled evolution in particle size distribution and optical depth spectra helps explain the relationship between the global maps of 0.5- and 1.0-kilometer optical depth derived from the AVHRR and SAGE satellite measurements. It also sets a context for evaluating remaining uncertainties in each of these satellite data products. We also show how the effects of wavelength-dependent refractive index on backscatter spectra can influence particle sizes retrieved from multiwavelength lidar measurements.

Russell, Philip B.↗
NASA NTRS1995

A Unified Picture of Pinatubo Aerosol Global-to Micro-Scale Evolution, From Space, Air, and Ground Measurements

We combine a variety of measurements to develop a composite picture of the post-Pinatubo aerosol and assess the consistency and uncertainties of the measurement and retrieval techniques. Satellite infrared spectroscopy, particle morphology, and evaporation temperature measurements are in accord with theoretical calculations in showing a dominant particle composition of H2SO4-H2O mixture, with H2SO4 weight fraction of 65-80% for most stratospheric temperatures and humidities. Important exceptions are: (1) the presence of volcanic ash at all altitudes initially and in a layer just above the tropopause until at least March 1992, and (2) much smaller H2SO4 weight fractions at the low temperatures attained in high latitude winters and at the tropical tropopause, Laboratory spectroscopy and theoretical calculations yield wavelength- and temperature-dependent refractive indices for the dominant H2SO4-H2O droplets. These in turn permit derivation of particle size spectra from measured optical depth spectra, for comparison to direct measurements by impactors and optical counters. All three techniques paint a generally consistent picture of the evolution of R(sub eff), the effective, or area-weighted, particle radius. In the first month after the eruption, although particle numbers increased by orders of magnitude, R(sub eff) was similar to the preemption value of 0.1 to 0.2 microns, because both small (r less than 0.2 microns) and large (r greater than 0.6 micron particles increased in number. Over the next 3-6 months, R(sub eff) increased to about 0.5 microns reflecting particle growth through condensation and coagulation. In general, R(sub eff) continued to increase for about a year after the eruption. Extinction spectra computed from in situ size distribution measurements are consistent with optical depth measurements, which show spectra with maxima initially at wavelengths of 0.42 microns or less, and thereafter progressively increasing to between 0.78 and 1 micron. Not until 1993 do optical depth spectra begin to show a clear return to the preemption signature of maximizing at the shortest visible wavelengths or in the near UV. This coupled evolution in particle size distribution and optical depth spectra helps explain the relationship between the global maps of 0.5- 1.0- micron optical depth derived from the AVHRR and SAGE satellite measurements.

Russell, Philip B.↗
NASA NTRS2002

Low Resolution Picture Transmission (LRPT) Demonstration System

Low-Resolution Picture Transmission (LRPT) is a proposed standard for direct broadcast transmission of satellite weather images. This standard is a joint effort by the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) and the National Oceanic Atmospheric Administration (NOAA). As a digital transmission scheme, its purpose is to replace the current analog Automatic Picture Transmission (APT) system for use in the Meteorological Operational (METOP) satellites. Goddard Space Flight Center has been tasked to build an LRPT Demonstration System (LDS). It's main objective is to develop or demonstrate the feasibility of a low-cost receiver utilizing a Personal Computer (PC) as the primary processing component and determine the performance of the protocol in the simulated Radio Frequency (RF) environment. The approach would consist of two phases. In the phase 1, a Commercial-off-the-Shelf (COTS) Modulator-Demodulator (MODEM) board that would perform RF demodulation would be purchased allowing the Central Processing Unit (CPU) to perform the Consultative Committee for Space Data Systems (CCSDS) protocol processing. Also since the weather images are compressed the PC would perform the decompression. Phase 1 was successfully demonstrated on December 1997. Phase 2 consists of developing a high-fidelity receiver, transmitter and environment simulator. Its goal is to find out how the METOP Specification performs in a simulated noise environment in a cost-effective receiver. The approach would be to produce a receiver using as much software as possible to perform front-end processing to take advantage of the latest high-speed PCs. Thus the COTS MODEM used in Phase 1 is performing RF demodulation along with data acquisition providing data to the receiving software. Also, environment simulator is produced using the noise patterns generated by Institute for Telecommunications Sciences (ITS) from their noise environment study.

Fong, Wai↗
NASA NTRS2002

Low Resolution Picture Transmission (LRPT) Demonstration System

Low-Resolution Picture Transmission (LRPT) is a proposed standard for direct broadcast transmission of satellite weather images. This standard is a joint effort by the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) and NOAA. As a digital transmission scheme, its purpose is to replace the current analog Automatic Picture Transmission (APT) system for use in the Meteorological Operational (METOP) satellites. GSFC has been tasked to build an LRPT Demonstration System (LDS). Its main objective is to develop or demonstrate the feasibility of a low-cost receiver utilizing a PC as the primary processing component and determine the performance of the protocol in the simulated Radio Frequency (RF) environment. The approach would consist of two phases.

Fong, Wai↗
NASA NTRS1965

PCM picture transmission.

PCM picture transmission, pseudorandom scanning, noise, bandwidth compression and digital simulation

BANDWIDTH↗
NASA NTRS1967

Picture coding.

Picture coding systems and selection of pre- and post-quantizing filters

PICTURE↗