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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Gravity Waves

In recent years it has been widely recognized that vertically propagating gravity waves play an important role in the dynamics of the middle atmosphere in partly determining the large scale temperature and wind structure through their energy and momentum transport. In particular, the meridional temperature distribution and the mean wind profile in the upper mesosphere are considered to be largely affected by the turbulence diffusion and friction that gravity waves induce through their breaking. For an understanding of the middle atmosphere circulation, it is therefore very important to know the global distribution and temporal variation of gravity waves in a climatological sense. The results of the statistics for gravity wave activity in the stratosphere and mesosphere are presented as a function of latitude and month, with the aid of meteorological rocket network observations.

Hirota, I.↗
NASA NTRS1988

Interferometric synthetic aperture microwave radiometry for the remote sensing of the earth

Interferometric aperture synthesis is presented as an alternative to real aperture measurements of the earth's brightness temperature from low earth orbit. The signal-to-noise performance of a single interferometric measurement is considered, and the noise characteristics of the brightness temperature image produced from the interferometer measurements are discussed. The sampling requirements of the measurements and the resulting effects of the noise in the measurements on the image are described. The specific case of the electronically steered thinned array radiometer (ESTAR) currently under construction is examined. The ESTAR prototype is described in detail sufficient to permit a performance evaluation of its spatial and temperature resolution. Critical aspects of an extension of the ESTAR sensor to a larger spaceborne system are considered. Of particular importance are the number and placement of antenna elements in the imaging array. A comparison of the implementation methodologies of radio astronomy and earth remote sensing is presented along with the effects of the source brightness distribution, the antenna array configuration and the method used for array scanning.

Ruf, Christopher S.↗
NASA NTRS2001

Damage Assessment of Creep Tested and Thermally Aged Metallic Alloys Using Acousto-Ultrasonics

In recent years emphasis has been placed on the early detection of material changes experienced in turbine powerplant components. During the scheduled overhaul of a turbine, the current techniques of examination of various hot section components aim to find flaws such as cracks, wear, and erosion, as well as excessive deformations. Thus far, these localized damage modes have been detected with satisfactory results. However, the techniques used to find these flaws provide no information on life until the flaws are actually detected. Major improvements in damage assessment, safety, as well as more accurate life prediction could be achieved if nondestructive evaluation (NDE) techniques could be utilized to sense material changes that occur prior to the localized defects mentioned. Because of elevated temperatures and excessive stresses, turbine components may experience creep behavior. As a result, it is desirable to monitor and access the current condition of such components. Research at the NASA Glenn Research Center involves developing and utilizing an NDE technique that discloses distributed material changes that occur prior to the localized damage detected by the current methods of inspection. In a recent study, creep processes in a nickel-base alloy were the life-limiting condition of interest, and the NDE technique was acousto-ultrasonics (AU). AU is an NDE technique that utilizes two ultrasonic transducers to interrogate the condition of a test specimen. The sending transducer introduces an ultrasonic pulse at a point on the surface of the specimen while a receiving transducer detects the signal after it has passed through the material. The goal of the method is to correlate certain parameters of the detected waveform to characteristics of the material between the two transducers. Here, the waveform parameter of interest is the attenuation due to internal damping for which information is being garnered from the frequency domain. The parameters utilized to indirectly quantify the attenuation are the ultrasonic decay rate as well as various moments of the frequency power spectrum. A new, user-friendly, graphical interface AU system was developed at NASA Glenn. This system is an all-inclusive, multifunction system that controls the sending and receiving ultrasonic transducers as well as all posttest signal analysis. The system's postprocessing software calculates the multiple parameters used to study the material of interest.

Gyekenyesi, Andrew L.↗
NASA NTRS2013

Development of Advanced Seed Laser Modules for Lidar and Spectroscopy Applications

We report on recent progress made in the development of highly compact, single mode, distributed feedback laser (DFB) seed laser modules for lidar and spectroscopy applications from space based platforms. One of the intended application of this technology is in the NASA's Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) mission. The DFB laser modules operating at 1571 nm and 1262 nm have advanced current and temperature drivers built into them. A combination of temperature and current tuning allows coarse and fine adjustment of the diode wavelengths.

Prasad, Narasimha S.↗
NASA NTRS2014

Real-Time Closed Loop Modulated Turbine Cooling

It has been noted by industry that in addition to dramatic variations of temperature over a given blade surface, blade-to-blade variations also exist despite identical design. These variations result from manufacturing variations, uneven wear and deposition over the life of the part as well as limitations in the uniformity of coolant distribution in the baseline cooling design. It is proposed to combine recent advances in optical sensing, actuation, and film cooling concepts to develop a workable active, closed-loop modulated turbine cooling system to improve by 10 to 20 the turbine thermal state over the flight mission, to improve engine life and to dramatically reduce turbine cooling air usage and aircraft fuel burn. A reduction in oxides of nitrogen (NOx) can also be achieved by using the excess coolant to improve mixing in the combustor especially for rotorcraft engines. Recent patents filed by industry and universities relate to modulating endwall cooling using valves. These schemes are complex, add weight and are limited to the endwalls. The novelty of the proposed approach is twofold 1) Fluidic diverters that have no moving parts are used to modulate cooling and can operate under a wide range of conditions and environments. 2) Real-time optical sensing to map the thermal state of the turbine has never been attempted in realistic engine conditions.

turbines↗
NASA NTRS2000

On the Feasibility of Studying Shortwave Aerosol Radiative Forcing of Climate Using Dual-Wavelength Aerosol Backscatter Lidar

The current low confidence in the estimates of aerosol-induced perturbations of Earth's radiation balance is caused by the highly non-uniform compositional, spatial and temporal distributions of tropospheric aerosols on a global scale owing to their heterogeneous sources and short lifetimes. Nevertheless, recent studies have shown that the inclusion of aerosol effects in climate model calculations can improve agreement with observed spatial and temporal temperature distributions. In light of the short lifetimes of aerosols, determination of their global distribution with space-borne sensors seems to be a necessary approach. Until recently, satellite measurements of tropospheric aerosols have been approximate and did not provide the full set of information required to determine their radiative effects. With the advent of active aerosol remote sensing from space (e.g., PICASSO-CENA), the applicability fo lidar-derived aerosol 180 deg -backscatter data to radiative flux calculations and hence studies of aerosol effects on climate needs to be investigated.

Redemann, Jens↗
NASA NTRS2011

A Pure Marine Aerosol Model, for Use in Remote Sensing Applications

Retrievals of aerosol optical depth (AOD) and related parameters from satellite measurements typically involve prescribed models of aerosol size and composition, and are therefore dependent on how well these models are able to represent the radiative behaviour of real aerosols, This study uses aerosol volume size distributions retrieved from Sun-photometer measurements at 11 Aerosol Robotic Network (AERONET) island sites, spread throughout the world's oceans, as a basis to define such a model for unpolluted maritime aerosols. Size distributions are observed to be bimodal and approximately lognormal, although the coarse mode is skewed with a long tail on the low-radius end, The relationship of AOD and size distribution parameters to meteorological conditions is also examined, As wind speed increases, so do coarse-mode volume and radius, The AOD and Angstrom exponent (alpha) show linear relationships with wind speed, although there is considerable scatter in all these relationships, limiting their predictive power. Links between aerosol properties and near-surface relative humidity, columnar water vapor, and sea surface temperature are also explored. A recommended bimodal maritime model, which is able to reconstruct the AERONET AOD with accuracy of order 0.01-0.02, is presented for use in aerosol remote sensing applications. This accuracy holds at most sites and for wavelengths between 340 nm and 1020 nm. Calculated lidar ratios are also provided, and differ significantly from those currently used in Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) processing.

Sayer, A. M.↗
NASA NTRS2012

Overview of US AID-World Bank-NASA Collaboration to Address Water Management Issues in the MENA Region

The World Bank, USAID and NASA have recently established a joint project to study multiple issues pertaining to water related applications in the Middle East North Africa (MENA) region. The main concentration of the project is on utilization of remote sensing data and hydrological models to address crop irrigation and mapping, flood mapping and forecasting, evapotranspiration and drought problems prevalent in this large geographic area. Additional emphases are placed on understanding the climate impact on these areas as well. Per IPCC 2007 report, by the end of this century MENA region is projected to experience an increase of 3 C to 5 C rise in mean temperatures and a 20% decline in precipitation. This poses a serious problem for this geographic zone especially when majority of the hydrological consumption is for the agriculture sector and the remaining amount is for domestic consumption. The remote sensing data from space is one of the best ways to study such complex issues and further feed into the decision support systems. NASA's fleet of Earth Observing satellites offer a great vantage point from space to look at the globe and provide vital signs necessary to maintain healthy and sustainable ecosystem. These observations generate multiple products such as soil moisture, global precipitation, aerosols, cloud cover, normalized difference vegetation index, land cover/use, ocean altimetry, ocean salinity, sea surface winds, sea surface temperature, ozone and atmospheric gases, ice and snow measurements, and many more. All of the data products, models and research results are distributed-via the Internet freely through out the world. This project will utilize several NASA models such as global Land Data Assimilation System (LDAS) to generate hydrological states and fluxes in near real time. These LDAS products will then be further compared with other NASA satellite observations (MODIS, VIIRS, TRMM, etc.) and other discrete models to compare and optimize evapotranspiration, soil moisture and crop irrigation, droUght assessment and water balance. The floods being a critical disaster in many of the MENA countries, NASA's global flood mapping and modeling framework (CREST) will be customized for country specific needs and delivered to the remote sensing organizations for their future use. Finally, capacity building is a critical part of this project and NASA will assist in this effort as well.

Habib, Shahid↗
NASA NTRS2017

Utilizing the Precessing Orbit of TRMM to Produce Hourly Corrections of Geostationary Infrared Imager Data with the VIRS Sensor

Accurate characterization of the Earth's radiant energy is critical for many climate monitoring and weather forecasting applications. For example, groups at the NASA Langley Research Center rely on stable visible- and infrared-channel calibrations in order to understand the temporal/spatial distribution of hazardous storms, as determined from an automated overshooting convective top detection algorithm. Therefore, in order to facilitate reliable, climate-quality retrievals, it is important that consistent calibration coefficients across satellite platforms are made available to the remote sensing community, and that calibration anomalies are recognized and mitigated. One such anomaly is the infrared imager brightness temperature (BT) drift that occurs for some Geostationary Earth Orbit satellite (GEOsat) instruments near local midnight. Currently the Global Space-Based Inter-Calibration System (GSICS) community uses the hyperspectral Infrared Atmospheric Sounding Interferometer (IASI) sensor as a common reference to uniformly calibrate GEOsat IR imagers. However, the combination of IASI, which has a 21:30 local equator crossing time (LECT), and hyperspectral Atmospheric Infrared Sounder (AIRS; 01:30 LECT) observations are unable to completely resolve the GEOsat midnight BT bias. The precessing orbit of the Tropical Rainfall Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS), however, allows sampling of all local hours every 46 days. Thus, VIRS has the capability to quantify the BT midnight effect observed in concurrent GEOsat imagers. First, the VIRS IR measurements are evaluated for long-term temporal stability between 2002 and 2012 by inter-calibrating with Aqua-MODIS. Second, the VIRS IR measurements are assessed for diurnal stability by inter-calibrating with Meteosat-9 (Met-9), a spin-stabilized GEOsat imager that does not manifest any diurnal dependency. In this case, the Met-9 IR imager is first adjusted with the official GSICS calibration coefficients. Then VIRS is used as a diurnal calibration reference transfer to produce hourly corrections of GEOsat IR imager BT. For the 9 three-axis stabilized GEO imagers concurrent with VIRS, the midnight effect increased the BT on average by 0.5 K (11 microns) and 0.4 K (12 microns), with a peak at approx.01:00 local time. As expected, the spin-stabilized GEOsats revealed a smaller diurnal temperature cycle (mostly < 0.2 K) with inconsistent peak hours.

Scarino, Benjamin↗
NASA NTRS1990

Bias correction for rainrate retrievals from satellite passive microwave sensors

Rainrates retrieved from past and present satellite-borne microwave sensors are affected by a fundamental remote sensing problem. Sensor fields-of-view are typically large enough to encompass substantial rainrate variability, whereas the retrieval algorithms, based on radiative transfer calculations, show a non-linear relationship between rainrate and microwave brightness temperature. Retrieved rainrates are systematically too low. A statistical model of the bias problem shows that bias correction factors depend on the probability distribution of instantaneous rainrate and on the average thickness of the rain layer.

Short, David A.↗
NASA NTRS1998

Development of Advanced Laser Diode Sources

The design and operation of InGaAs-GaAs-AlGaAs asymmetric cladding ridge waveguide distributed Bragg reflector lasers is presented. Targeted for the remote sensing of water vapor with absorption lines in the lambda approximately 930 nm region, these devices operate CW with threshold currents as low as 11 MA and slope efficiencies as high as 0.37 W/A. Tbey also operate with over 30-dB side-mode suppression, and the typical CW characteristic temperature, T(sub o), is 95 K.

Coleman, J. J.↗
NASA NTRSDate not supplied

Differential absorption lidar (DIAL) for water vapor and aerosol profiling from airborne and space-based platforms

Many current challenges in weather and climate prediction involve cloud and aerosol processes, which are intimately linked to processes that initiate or take place within the planetary boundary layer (PBL). The current space-based observing system provides a wealth of information on the spatial distribution of key atmospheric variables such as profiles of water vapor (WV) and temperature, but lacks the sensitivity, accuracy, and vertical resolution in the PBL to overcome the observational gaps that inhibit the parametrization and advancement of current climate and weather models. To overcome some of these observational gaps and improve understanding and monitoring of these key processes, mature remote sensing techniques like Differential Absorption Lidar (DIAL) can be employed from various platforms to capture processes on a wide range of spatial scales. This presentation will provide an overview of NASA’s water vapor DIAL capabilities, present the strengths, weaknesses, and synergies of the DIAL technique relative to traditional methods, and provide representative data examples from the HALO airborne water vapor DIAL which was designed as a technology testbed for future space-based DIAL missions as well as a workhorse instrument in support of suborbital process studies. HALO is an airborne multifunction lidar system, simultaneously profiling WV with the DIAL technique and aerosol and cloud optical properties and PBL heights via the high spectral resolution lidar (HSRL) technique. HALO has a compact design that allows it to fly on most research aircraft, enabling nadir profiling from the lower stratosphere down through the PBL, which is critical for studying processes such as convection and cloud formation that can link the PBL and free troposphere. We will end with an outlook on the benefits and challenges of transitioning the mature DIAL technique to space to compliment other active and passive sounders and enable new PBL observations for the future Earth Observing System. The Atmospheric Boundary layer Lidar pathfindEr (ABLE), a program aimed at advancing technologies to enable the first demonstration of DIAL from space with cross-cutting observables of PBL heights, aerosol and cloud profiling, and methane columns from space will also be presented.

Brian J. Carroll↗
NASA NTRS1985

Remote sensing of atmosphere-surface interaction parameters

Examples are given of the accuracy of the results obtained from the HIRS 2/MSU (High Resolution Infrared Sounder and Microwave Sounding Unit) analysis of ocean, atmosphere, and land parameters. Sea surface temperatures are compared with available ship and buoy radiosonde data, and land surface temperatures are compared with shelter temperatures. The seasonal change in land and ocean skin surface temperature is reviewed. The distribution of clouds is examined and their opacities in the visible and infrared parts of the spectrum are compared.

Chahine, M. T.↗
NASA NTRS1990

Application of high stability oscillators to radio science experiments using deep space probes

The microwave telecommunication links between the earth and deep space probes have long been used to conduct radio science experiments which take advantage of the phase coherency and stability of these links. These experiments measure changes in the phase delay of the signals to infer electrical, magnetic and gravitational properties of the solar system environment and beyond through which the spacecraft and radio signals pass. The precision oscillators, from which the phase of the microwave signals are derived, play a key role in the stability of these links and therefore the sensitivity of these measurements. These experiments have become a driving force behind recent and future improvements in the Deep Space Network and spacecraft oscillators and frequency and time distribution systems. Three such experiments which are key to these improvements are briefly discussed and relationship between their sensitivity and the signal phase stability is described. The first is the remote sensing of planetary atmospheres by occultation in which the radio signal passes through the atmosphere and is refracted causing the signal pathlength to change from which the pressure and the temperature of the atmosphere can be derived. The second experiment is determination of the opacity of planetary rings by passage of the radio signals through the rings. The third experiment is the research for very low frequency gravitational radiation. The fractional frequency variation of the signal is comparable to the spatial strain amplitude the system is capable of detecting. A summary of past results and future possibilities for these experiments are presented.

Kursinski, Emil R.↗
NASA NTRS2017

AIRS-Only Product in Giovanni for Exploring Up-to-Date AIRS Observation and Comparing with AIRS+AMSU Product

The NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) has been the home of processing, archiving, and distribution services for the Atmospheric Infrared Sounder (AIRS) mission since its launch in 2002 for global observations of the atmospheric state. Giovanni, a Web-based application developed by the GES DISC, provides a simple and intuitive way to visualize, analyze, and access vast amounts of Earth science remote sensing data without having to download the data. Most important AIRS variables, including temperature and humidity profiles, outgoing longwave radiation, cloud properties, and trace gases, are available in Giovanni. AIRS is an instrument suite comprised of a hyperspectral infrared instrument (AIRS) and two multichannel microwave instruments, the Advanced Microwave Sounding Unit (AMSU) and the Humidity Sounder for Brazil (HSB). As HSB ceased operation in the very early stages of the AIRS mission, the AIRS project operates two parallel retrieval algorithms: one using both IR and MW measurements (AIRS+AMSU) and the other using only IR measurements (AIRS-only), which covers most of the mission duration. The AIRS+AMSU product is better quality, and the variables in Giovanni are from this product. However, generation of the AIRS+AMSU product has been suspended since the AMSU instrument anomaly occurred in late September 2016. To continue exploring up-to-date AIRS observations, the same set of variables from the AIRS-only product have been added to Giovanni by the GES DSIC. This will also support comparison of AIRS-only with AIRS+AMSU retrievals. In this presentation, we demonstrate the visualization of the AIRS-only product and plots/statistics of comparison with AIRS+AMSU product using Giovanni.

AIRS↗
NASA NTRS2017

Assessment of the Impact of Spatial Heterogeneity on Microwave Satellite Soil Moisture Periodic Error

An accurate temporal and spatial characterization of errors is required for the efficient processing, evaluation, and assimilation of remotely-sensed surface soil moisture retrievals. However, empirical evidence exists that passive microwave soil moisture retrievals are prone to periodic artifacts which may complicate their application in data assimilation systems (which commonly treat observational errors as being temporally white). In this paper, the link between such temporally-periodic errors and spatial land surface heterogeneity is examined. Both the synthetic experiment and site-specified cases reveal that, when combined with strong spatial heterogeneity, temporal periodicity in satellite sampling patterns (associated with exact repeat intervals of the polar-orbiting satellites) can lead to spurious high frequency spectral peaks in soil moisture retrievals. In addition, the global distribution of the most prominent and consistent 8-day spectral peak in the Advanced Microwave Scanning Radiometer - Earth Observing System soil moisture retrievals is revealed via a peak detection method. Three spatial heterogeneity indicators - based on microwave brightness temperature, land cover types, and long-term averaged vegetation index - are proposed to characterize the degree to which the variability of land surface is capable of inducing periodic error into satellite-based soil moisture retrievals. Regions demonstrating 8-day periodic errors are generally consistent with those exhibiting relatively higher heterogeneity indicators. This implies a causal relationship between spatial land surface heterogeneity and temporal periodic error in remotely-sensed surface soil moisture retrievals.

Fangni Lei↗
NASA NTRS1986

Remote sensing of land-surface temperature from HIRS/MSU data

A relaxation algorithm which permits meteorological parameters to be obtained from satellite data, without a priori assumptions about the properties of the other unknowns in the field of view, was developed. Atmospheric temperature profiles, atmospheric humidity, cloud cover, cloud top height, cloud top temperature, sea-surface temperature, land-surface temperature, snow cover, and ice cover are derived. Simultaneous determination of atmospheric and surface thermal structure and the cloud distribution provides information on heat sources and sinks, storage rates, and transport phenomena in the atmosphere. Such information is critical in determining the driving mechanisms for motions in the atmosphere and oceans and in improving numerical weather prediction.

Chahine, M. T.↗
NASA NTRSDate not supplied

Remote Sensing of Clouds, Water Vapor, and Near-Surface Winds Under Various Aerosol Conditions During CAMP2Ex

The Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) field campaign took place from August – October 2019. CAMP2Ex science objectives include understanding aerosol-cloud interaction under various Meteorological conditions, and how these Meteorological phenomena affect aerosol distribution in the atmosphere. Numerous instruments were flown on the National Aeronautics and Space Administration (NASA) P-3 aircraft during 19 CAMP2Ex science flights, including the Advanced Microwave Precipitation Radiometer (AMPR) the Airborne Third Generation Precipitation Radar (APR-3), and the High Spectral Resolution Lidar 2 (HSRL2). Geophysical retrieval equations for cloud liquid water, columnar water vapor, and near-surface wind speed using AMPR brightness temperatures have been derived and tested using CAMP2Ex data. Water vapor and wind speed retrievals have been validated using in situ observations, such as dropsondes and shipborne instruments. This presentation will demonstrate these AMPR-based retrievals during CAMP2Ex, including discussions of retrieval uncertainties. Specific CAMP2Ex flights will be presented in greater detail, including inferences of other Meteorological phenomena in clear air and around precipitating and non-precipitating clouds, such as background wind speeds and potential identification of gust fronts. These analyses will be supplemented with APR-3 reflectivity and Doppler velocity data to infer microphysical processes occurring within and around selected clouds of interest. In cases where multiple remote-sensing measurements were obtained for the same cloud, a time-evolution analysis of these features may be performed. Throughout these analyses, HSRL2 data will be used to quantify aerosol properties beneath the P-3, and variations in the AMPR/APR-3 observations with respect to various aerosol conditions will be discussed.

Corey Amiot↗