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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Validation of a technique for estimating outgoing longwave radiation from HIRS radiance observations

Simultaneous observations by the Earth Radiation Budget Experiment (ERBE) scanning radiometer and the High-Resolution Infrared Sounder (HIRS) on board the NOAA-9 spacecraft have been used to validate a multispectral technique for estimating the outgoing longwave radiation (OLR) from the earth-atmosphere system. Results from approximately 100 000 collocated observations show that the HIRS technique provides instantaneous OLR estimates that agree with the ERBE observations just as well as different ERBE scanners agree with each other--about 5 W m(exp -2) rms. Although there are differences between the HIRS and ERBE estimates that depend upon the scene type and time of day, the HIRS technique explained more than 99% of the variance of the ERBE observations for both day and night observations. The results suggest that the HIRS OLR technique is a suitable replacement for the Advanced Very High Resolution Radiometer technique now used by the National Oceanic and Atmospheric Administration for operational estimates of the OLR.

Ellingson, Robert G.↗
NASA NTRS1992

Cloud-property retrieval using merged HIRS and AVHRR data

A technique is developed that uses a multispectral, multiresolution method to improve the overall retrieval of mid- to high-level cloud properties by combining HIRS sounding channel data with higher spatial resolution AVHRR radiometric data collocated with the HIRS footprint. Cirrus cloud radiative and physical properties are determined using satellite data, surface-based measurements provided by rawinsondes and lidar, and aircraft-based lidar data collected during the First International Satellite Cloud Climatology Program Regional Experiment in Wisconsin during the months of October and November 1986. HIRS cloud-height retrievals are compared to ground-based lidar and aircraft lidar when possible. Retrieved cloud heights are found to have close agreement with lidar for thin cloud, but are higher than lidar for optically thick cloud. The results of the reflectance-emittance relationships derived are compared to theoretical scattering model results for both water-droplet spheres and randomly oriented hexagonal ice crystals. It is found that the assumption of 10-micron water droplets is inadequate to describe the reflectance-emittance relationship for the ice clouds seen here. Use of this assumption would lead to lower cloud heights using the ISCCP approach. The theoretical results show that use of hexagonal ice crystal phase functions could lead to much improved results for cloud retrieval algorithms using a bispectral approach.

Baum, Bryan A.↗
NASA NTRS2012

An Alternative Inter-Satellite Calibration of the UMD HIRS OLR Retrievals

Outgoing Longwave Radiation (OLR) at the top-of-atmosphere (TOA) is a fundamental component of Earth's energy balance and represents the heat energy in the thermal bands rejected to space by the planet. Determination of OLR from satellites has a long and storied history, but the observational record remains largely fragmented with gaps in satellite measurements over the past three decades. Perhaps the most semi-continuous set of retrievals comes from the University of Maryland (UMD) algorithm that uses four HIRS (High Resolution Infrared Sounder) channels on the NOAA polar orbiting satellites to estimate OLR. This data set shows great promise in helping to bridge the discontinuous ERBS (Earth Radiation Budget Satellite) and CERES (Clouds and the Earth s Radiant Energy System) measurements. However, significant satellite inter-calibration biases persist with the present UMD data, principally outside the tropics. Difficulties relate to the combination of drift of the satellite equator crossing time through the diurnal cycle and changes in HIRS channel response function design. Here we show how an ad hoc recalibration of the UMD retrievals among the different satellites removes much of the remaining uncertainty due to diurnal drift of the satellite orbit. The adjusted HIRS data (using no other external information) show much better agreement with OLR from the European Center Interim Reanalysis (EC-Int), longer-term signals in the Global Energy and Water Cycle Experiment / Surface Radiation Budget (GEWEX/SRB) retrievals, and also agree well with ERBS and CERES OLR measurements. These results augur well for narrowing the uncertainties in multi-decadal estimates of this important climate variable.

Robertson, Franklin R.↗
NASA NTRS1982

Dynamic analysis of turbulent annular seals based on Hirs' lubrication equation

Expressions are derived which define dynamic coefficients for high-pressure annular seals typical of neck-ring and interstage seals employed in multistage centrifugal pumps. Completely developed turbulent flow is assumed in both the circumferential and axial directions, and is modeled in this analysis by Hirs' turbulent lubrication equations. Linear zeroth and first-order 'short-bearing' perturbation solutions are developed by an expansion in the eccentricity ratio. The influence of inlet swirl is accounted for in the development of the circumferential flow field. Comparisons are made between the stiffness, damping, and inertia coefficients derived herein based on Hirs' model and previously published results based on other models. Finally, numerical results are presented for interstage seals in the Space Shuttle Main Engine High Pressure Fuel Turbopump and a water pump.

Childs, D. W.↗
NASA NTRS1987

Comparison of Hirs' equation of Moody's equation for determining rotordynamic coefficients of annular pressure seals

The rotordynamic coefficients of an incompressible-flow annular pressure seal were determined using a bulk-flow model in conjunction with two different friction factor relationships. The first, Hirs' equation, assumes the friction factor is a function of Reynolds number only. The second, Moody's equation, approximates Moody's diagram and assumes the friction factor is a function of both Reynolds number and relative roughness. For each value of relative roughness, Hirs' constants were determined so that both equations gave the same magnitude and slope of the friction factor. For smooth seals, both relationships give the same results. For rough seals (e/2 H sub 0 = 0.05) Moody's equation predicts 44% greater direct stiffness, 35% greater cross-coupled stiffness, 19% smaller cross-coupled damping, 59% smaller cross-coupled inertia, and nominally the same direct damping and direct inertia.

Nelson, Clayton C.↗
NASA NTRS1986

Comparison of Hirs' equation with Moody's equation for determining rotordynamic coefficients of annular pressure seals

The rotordynamic coefficients of an incompressible-flow annular pressure seal were determined using a bulk-flow model in conjunction with two different friction factor relationships. The first, Hirs' equation, assumes the friction factor is a function of Reynolds number only. The second, Moody's equation, approximates Moody's diagram and assumes the friction factor is a function of both Reynolds number and relative roughness. For each value of relative roughness, Hirs' constants were determined so that both equations gave the same magnitude and slope of the friction factor. For smooth seals, both relationships give the same results. For rough seals, Moody's equation predicts 44 percent greater direct stiffness, 35 percent greater cross-coupled stiffness, 19 percent smaller cross-coupled damping, 59 percent smaller cross-coupled inertia, and nominally the same direct damping and direct inertia.

Nelson, C. C.↗
NASA NTRS1990

An analysis of cloud property retrieval using HIRS-2 and AVHRR radiometric data

The principal advantage of the HIRS cloud height retrieval is to provide an unbiased estimate of cloud height for optically thin, high cloud. This capability is employed to examine the relationship of cirrus visible reflectance to thermal IR emittance. By combining data from the HIRS-2 and AVHRR instruments on the NOAA operational satellites the proposed method attempts to improve the ability of existing satellite radiometers to recover information on middle-level and high-level clouds. This combination of data sets leads to an improved cloud recovery algorithm for the detection and analysis of cirrus clouds.

Baum, Bryan A.↗
NASA NTRS1994

Multilevel cloud retrieval using multispectral HIRS and AVHRR data: Nighttime oceanic analysis

A multispectral, multiresolution (MSMR) method is developed for analyzing scenes of overlapping cloud layers. The MSMR method is applied to data from the NOAA 11 advanced very high resolution radiometer (AVHRR) and the high-resolution infrared radiometer sounder (HIRS-2). The data are from a nighttime oceanic scene in which a semitransparent cirrus veil overlays a large-scale stratus cloud. Low-cloud and clear-sky radiances are determined using a spatial coherence technique. Middle to upper level cloud pressures and radiances are estimated from HIRS-2 15 micrometer CO2 band radiometric data. The MSMR method improves the interpretation of a nighttime, oceanic scene containing thin cirrus over a large-scale stratiform cloud. If, for example, the same scene is analyzed using only the AVHRR 10.8 micrometer channel, the accompanying retrieved cloud heights are found to be between the cirrus and stratus cloud heights and are incorrectly identified as midlevel altostratus clouds. Theoretical radiative transfer model results for both water droplet spheres and randomly oriented hexagonal ice crystals are compared to observed AVHRR brightness temperature differences (BTD) between the 3.7- and 10.8 micrometer channels (BTD(sup 34)) and between the 10.8- and 12- micrometer channels (BTD(sup 45)) to distinguish among the effects of cloud optical depth, particle size, and phase for both single-layer clouds and overlapping two-layer clouds. Theoretical BTD calculations are used to estimate the range of effective particle sizes for eac h cloud layer. The data for the cirrus in the case study region near Bermuda are consistent with theoretical results for relatively small randomly oriented hexagonal ice crystals. The observed BTD(sup 34) and BTD(sup 45) values are lower for the cirrus above a lower-level cloud than for single-level cirrus with no underlying cloud. In certain cases the BTD analysis provides a way to distinguish between clouds composed of supercooled water droplets rather than ice particles. Analysis of nighttime data permits determination of stratus infrared optical depths smaller than 4.

Baum, Bryan A.↗
NASA NTRS1975

High Resolution Infrared Radiation Sounder (HIRS) for the Nimbus F Spacecraft

Flown on Nimbus F in June 1975, the high resolution infrared radiation sounder (HIRS) scans with a geographical resolution of 23KM and samples radiance in seventeen selected spectral channels from visible (.7 micron) to far IR (15 micron). Vertical temperature profiles and atmospheric moisture content can be inferred from the output. System operation and test results are described.

Koenig, E. W.↗
NASA NTRS1981

Visible infrared spin-scan radiometer atmospheric sounder radiometric calibration - An inflight evaluation from intercomparisons with HIRS and radiosonde measurements

The ability to conduct soundings from a geostationary platform has been demonstrated with the Visible IR spin-scan radiometer Atmospheric Sounder (VAS) aboard GOES-4. While a negative offset reaching 2.0-3.0 C for the upper atmospheric CO2 bands of VAS was observed in comparisons with High Resolution IR Radiation Sounder (HIRS) measurements and analyses of radiosonde data, VAS radiances are consistent with that material. After removing the offset, the temperature profiles derived from VAS radiances agree very well with those observed by radiosondes. Time variations in the atmospheric state are discernible from VAS soundings at three-hour intervals, and were confirmed by radiosonde observations.

Menzel, W. P.↗
NASA NTRS1982

HIRS-AMTS satellite sounding system test - Theoretical and empirical vertical resolving power

The present investigation is concerned with the vertical resolving power of satellite-borne temperature sounding instruments. Information is presented on the capabilities of the High Resolution Infrared Radiation Sounder (HIRS) and a proposed sounding instrument called the Advanced Moisture and Temperature Sounder (AMTS). Two quite different methods for assessing the vertical resolving power of satellite sounders are discussed. The first is the theoretical method of Conrath (1972) which was patterned after the work of Backus and Gilbert (1968) The Backus-Gilbert-Conrath (BGC) approach includes a formalism for deriving a retrieval algorithm for optimizing the vertical resolving power. However, a retrieval algorithm constructed in the BGC optimal fashion is not necessarily optimal as far as actual temperature retrievals are concerned. Thus, an independent criterion for vertical resolving power is discussed. The criterion is based on actual retrievals of signal structure in the temperature field.

Thompson, O. E.↗
NASA NTRS1981

HIRS-AMTS satellite sounding system test - Vertical resolving power

The present investigation is concerned with the vertical resolving power of satellite borne temperature sounding instruments. Specifically, information is presented on the capabilities of the High Resolution Infra-red Radiation Sounder (HIRS) and a proposed sounding instrument called the Advanced Meteorological Temperature Sounder (AMTS). Two quite different methods for assessing the vertical resolving power of satellite sounders are discussed, taking into account the theoretical method of Conrath (1972), and an independent criterion for vertical resolving power which is based on actual retrievals of signal structure in the temperature field. Some discrepancies are found between theory and retrieval tests. The results indicate that the theoretical Backus and Gilbert spread function does not represent the shortest resolvable length scale for a retrieval system.

Thompson, O. E.↗
NASA NTRS1984

Comparison of AMSU temperature soundings with those produced by HIRS and AMTS

The new generation of satellite borne radiometers to be launched in the late 1980's or early 1990's are currently planned to have as their main temperature sounding unit the AMSU (Advanced Microwave Sounding Unit). This device consists of two units, one of which contains 11 high spectral and spatial resolution channels which are to be used to produce vertical atmospheric temperature soundings. Other channels are to be used to determine atmospheric liquid water and water vapor amounts, as rain detectors, and for surface emissivity determination. This report, however, shall deal only with the accuracy of temperature retrievals. Toward this end studies have been carried out in which atmospheric temperature profiles were retrieved from simulated radiances for the AMSU channels. As a comparison, atmospheric temperature profiles were retrieved from simulated radiances for the currently operational HIRS infrared sounder as well as the proposed advanced infrared sounder AMTS. All simulations were based on a set of 400 mid-latitude radiosondes.

Reuter, D.↗
NASA NTRS1994

Four years of global cirrus cloud statistics using HIRS

Trends in global upper-tropospheric transmissive cirrus cloud cover are beginning to emerge from a four-year cloud climatology using NOAA polar-orbiting High-Resolution Infrared Radiation Sounder (HIRS) multispectral data. Cloud occurrence, height, and effective emissivity are determined with the CO2 slicing technique on the four years of data (June 1989-May 1993). There is a global preponderance of transmissive high clouds, 42% on the average; about three-fourths of these are above 500 hPa and presumed to be cirrus. In the Inter-tropical Convergence Zone (ITCZ), a high frequency of cirrus (greater than 50%) is found at all times; a modest seasonal movement tracks the sun. Large seasonal changes in cloud cover occur over the oceans in the storm belts at midlatitudes; the concentrations of these clouds migrate north and south with the seasons following the progressions of the subtropical highs (anticyclones). More cirrus is found in the summer than in the winter in each hemisphere. A significant change in cirrus cloud cover occurs in 1991, the third year of the study. Cirrus observations increase from 35% to 43% of the data, a change of eight percentage points. Other cloud forms, opaque to terrestrial radiation, decerase by nearly the same amount. Most of the increase is thinner cirrus with infrared optical depths below 0.7. The increase in cirrus happens at the same time as the 1991-92 El Nino/Southern Oscillation (ENSO) and the eruption of Mt. Pinatubo. The cirrus changes occur at the start of the ENSO and persist into 1993 in contrast to other climatic indicators that return to near pre-ENSO and volcanic levels in 1993.

Wylie, Donald P.↗
NASA NTRS1991

Two Years of Global Cirrus Cloud Statistics Using HIRS

A climatology of upper tropospheric semi-transparent cirrus clouds has been compiled using HIRS multispectral infrared data, sensitive to CO2 absorption, from the NOAA polar orbiting satellites. This is a report on the two years of data analyzed (June 1989 - May 1991). Semi-transparent clouds were found in 36% of the observations. Large seasonal changes were found in these clouds in many geographical areas; large changes occur in areas dominated by the ITCZ, the sub-tropical high pressure systems, and the mid-latitude storm belts. Semi-transparent clouds associated with these features move latitudinally with the seasons. These clouds also are more frequent in the summer hemisphere than the winter hemisphere. They appear to be linked to convective cloud development and the mid-latitudinal frontal weather systems. However, very thin semi-transparent cirrus has less seasonal movement than other cloud forms.

POLAR ORBIT TRAJECTORIES↗
NASA NTRS2000

Radiance and Jacobian Intercomparison of Radiative Transfer Models Applied to HIRS and AMSU Channels

The goals of this study are the evaluation of current fast radiative transfer models (RTMs) and line-by-line (LBL) models. The intercomparison focuses on the modeling of 11 representative sounding channels routinely used at numerical weather prediction centers: 7 HIRS (High-resolution Infrared Sounder) and 4 AMSU (Advanced Microwave Sounding Unit) channels. Interest in this topic was evidenced by the participation of 24 scientists from 16 institutions. An ensemble of 42 diverse atmospheres was used and results compiled for 19 infrared models and 10 microwave models, including several LBL RTMs. For the first time, not only radiances, but also Jacobians (of temperature, water vapor and ozone) were compared to various LBL models for many channels. In the infrared, LBL models typically agree to within 0.05-0.15 K (standard deviation) in terms of top-of-the-atmosphere brightness temperature (BT). Individual differences up to 0.5 K still exist, systematic in some channels, and linked to the type of atmosphere in others. The best fast models emulate LBL BTs to within 0.25 K, but no model achieves this desirable level of success for all channels. The ozone modeling is particularly challenging, In the microwave, fast models generally do quite well against the LBL model to which they were tuned. However significant differences were noted among LBL models, Extending the intercomparison to the Jacobians proved very useful in detecting subtle and more obvious modeling errors. In addition, total and single gas optical depths were calculated, which provided additional insight on the nature of differences. Recommendations for future intercomparisons are suggested.

Garand, L.↗
NASA NTRS2000

Radiance and Jacobian Intercomparison of Radiative Transfer Models Applied to HIRS and AMSU Channels

The goals of this study are the evaluation of current fast radiative transfer models (RTMs) and line-by-line (LBL) models. The intercomparison focuses on the modeling of 11 representative sounding channels routinely used at numerical weather prediction centers: seven HIRS (High-resolution Infrared Sounder) and four AMSU (Advanced Microwave Sounding Unit) channels. Interest in this topic was evidenced by the participation of 24 scientists from 16 institutions. An ensemble of 42 diverse atmospheres was used and results compiled for 19 infrared models and 10 microwave models, including several LBL RTMs. For the first time, not only radiances, but also Jacobians (of temperature, water vapor, and ozone) were compared to various LBL models for many channels. In the infrared, LBL models typically agree to within 0.05-0.15 K (standard deviation) in terms of top-of-the-atmosphere brightness temperature (BT). Individual differences up to 0.5 K still exist, systematic in some channels, and linked to the type of atmosphere in others. The best fast models emulate LBL BTs to within 0.25 K, but no model achieves this desirable level of success for all channels. The ozone modeling is particularly challenging. In the microwave, fast models generally do quite well against the LBL model to which they were tuned. However significant differences were noted among LBL models. Extending the intercomparison to the Jacobians proved very useful in detecting subtle and more obvious modeling errors. In addition, total and single gas optical depths were calculated, which provided additional insight on the nature of differences. Recommendations for future intercomparisons are suggested.

Garand, L.↗
NASA NTRS2012

An Alternative Inter-Satellite Calibration of the UMD HIRS OLR Retrievals

The observational record for determining Outgoing Longwave Radiation (OLR) from satellites remains largely fragmented with gaps over the past three decades among the Earth Radiation Budget Experiment (ERBE), Earth Radiation Budget Satellite (ERBS) and Clouds and the Earth s Radiant Energy System (CERES) measurements. Multi-band OLR retrievals are thus an important supplement to the broadband measurements. The most semi-continuous set of OLR retrievals comes from the University of Maryland (UMD) algorithm that uses four HIRS (High Resolution Infrared Sounder) channels on the NOAA polar orbiting satellites to estimate OLR. but residual biases due principally to diurnal drift of the polar orbiter platforms remain an issue. Here we show how an alternative recalibration of the UMD retrievals taking advantage of the relative diurnal drift rates between "morning" and "evening" satellite platforms removes much of the remaining uncertainty due to changes in equator crossing times.

Robertson, Franklin R.↗