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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

The beam filling error in the Nimbus 5 electronically scanning microwave radiometer observations of Global Atlantic Tropical Experiment rainfall

A comparison of rain rates retrieved from the Nimbus 5 electronically scanning microwave radiometer brightness temperatures and observed from shipboard radars during the Global Atlantic Tropical Experiment (GATE) phase I shows that the beam filling error is the major source of discrepancy between the two. When averaged over a large scene (the GATE radar array, 400 km in diameter), the beam filling error is quite stable, being 50 percent of the observed rain rate. This suggests the simple procedure of multiplying retrieved rain rates by 2 (correction factor). A statistical model of the beam filling error is developed by envisioning an idealized instrument field-of-view that encompasses an entire gamma distribution of rain rates. A modeled correction factor near 2 is found for rain rate and temperature characteristics consistent with GATE conditions. The statistical model also suggests that the correction factor varies from 1.5 to 2.5 for suppressed to enhanced tropical convective regimes, and decreases to 1.5 as the freezing level and average depth of the rain column decreases to 2.5 km.

Short, David A.↗
NASA NTRS1990

Science observations with the IUE using the one-gyro mode

The International Ultraviolet Explorer (IUE) attitude control system originally included an inertial reference package containing six gyroscopes for three axis stabilization. The science instrument includes a prime and redundant Field Error Sensor (FES) camera for target acquisition and offset guiding. Since launch, four of the six gyroscopes have failed. The current attitude control system utilizes the remaining two gyros and a Fine Sun Sensor (FSS) for three axis stabilization. When the next gyro fails, a new attitude control system will be uplinked which will rely on the remaining gyro and the FSS for general three axis stabilization. In addition to the FSS, the FES cameras will be required to assist in maintaining fine attitude control during target acquisition. This has required thoroughly determining the characteristics of the FES cameras and the spectrograph aperture plate as well as devising new target acquisition procedures. The results of this work are presented.

Imhoff, C.↗
NASA NTRS1992

Joint vector magnetograph observations at BBSO, Huairou Station and Mees Solar Observatory

Joint vector magnetograph observations were carried out at Big Bear Solar Observatory (BBSO), Huairou Solar Observing Station (Huairou), and Mees Solar Observatory (MSO) in late September 1989. Comparisons of vector magnetograms obtained at the three stations show a high degree of consistency in the morphology of both longitudinal and transverse fields. Quantitative comparisons show the presence of noise, cross-talk between longitudinal field and transverse field, Faraday rotation and signal saturation effects in the magnetograms. We have tried to establish how the scatter in measurements from different instruments is apportioned between these sources of error.

Wang, Haimin↗
NASA NTRS1990

Science observations with the IUE using the one-gyro mode

The International Ultraviolet Explorer (IUE) attitude control system originally included an inertial reference package containing six gyroscopes for three axis stabilization. The science instrument includes a prime and redundant Field Error Sensor (FES) camera for target acquisition and offset guiding. Since launch, four of the six gyroscopes have failed. The current attitude control system utilizes the remaining two gyros and a Fine Sun Sensor (FSS) for three axis stabilization. When the next gyro fails, a new attitude control system will be uplinked, which will relay on the remaining gyro and the FSS for general three axis stabilization. In addition to the FSS, the FES cameras will be required to assist in maintaining fine attitude control during target acquisition. This has required thoroughly determining the characteristics of the FES cameras and the spectrograph aperture plate as well as devising new target acquisition procedures. The results of this work are presented.

Imhoff, C.↗
NASA NTRS1938

Rate-of-climb Recorder

The chief advantage of the instrument lies in the degree of accuracy obtainable with suitably flexible capsule (dynamic pressure recorder with small test range) and in its sensitivity for recording static-pressure changes. A description and hook-up of the instrument is provided along with calculations of error.

Danielzig, Helmut↗
NASA NTRS1942

Aerodynamics of the Fuselage

The present report deals with a number of problems, particularly with the interaction of the fuselage with the wing and tail, on the basis of simple calculating method's derived from greatly idealized concepts. For the fuselage alone it affords, in variance with potential theory, a certain frictional lift in yawed flow, which, similar to the lift of a wing of small aspect ratio, is no longer linearly related to the angle of attack. Nevertheless there exists for this frictional lift something like a neutral stability point the position of which on oblong fuselages appears to be associated with the lift increase of the fuselage in proximity to the zero lift, according to the present experiments. The Pitching moments of the fuselage can be determined with comparatively great reliability so far as the flow conditions in the neighborhood of the axis of the fuselage can be approximated if the fuselage were absent, which, in general, is not very difficult. For the unstable contribution of the fuselage to the static longitudinal stability of the airplane it affords comparatively simple formulas, the evaluation of which offers little difficulty. On the engine nacelles there is, in addition a very substantial wing moment contribution induced by the nonuniform distribution of the transverse displacement flow of the nacelle along the wing chord; this also can be represented by a simple formula. A check on a large number of dissimilar aircraft types regarding the unstable fuselage and nacelle moments disclosed an agreement with the wind-tunnel tests, which should be sufficient for practical requirements. The errors remained throughout within the scope of instrumental accuracy.

Multhopp, H.↗
NASA NTRS2003

SIRTF Focal Plane Survey: A Pre-flight Error Analysis

This report contains a pre-flight error analysis of the calibration accuracies expected from implementing the currently planned SIRTF focal plane survey strategy. The main purpose of this study is to verify that the planned strategy will meet focal plane survey calibration requirements (as put forth in the SIRTF IOC-SV Mission Plan [4]), and to quantify the actual accuracies expected. The error analysis was performed by running the Instrument Pointing Frame (IPF) Kalman filter on a complete set of simulated IOC-SV survey data, and studying the resulting propagated covariances. The main conclusion of this study is that the all focal plane calibration requirements can be met with the currently planned survey strategy. The associated margins range from 3 to 95 percent, and tend to be smallest for frames having a 0.14" requirement, and largest for frames having a more generous 0.28" (or larger) requirement. The smallest margin of 3 percent is associated with the IRAC 3.6 and 5.8 micron array centers (frames 068 and 069), and the largest margin of 95 percent is associated with the MIPS 160 micron array center (frame 087). For pointing purposes, the most critical calibrations are for the IRS Peakup sweet spots and short wavelength slit centers (frames 019, 023, 052, 028, 034). Results show that these frames are meeting their 0.14" requirements with an expected accuracy of approximately 0.1", which corresponds to a 28 percent margin.

pointing↗
NASA NTRS2011

STEREO SECCHI COR1-A/B Intercalibration at 180 deg Separation

The twin Solar Terrestrial Relations Observatory (STEREO) spacecraft reached a separation angle of 180 degrees on 6 February 2011. This provided a unique opportunity to test the intercalibration between the Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) telescopes on both spacecraft for areas above the limb. So long as the corona is optically thin, at 180 degree separation each spacecraft sees the same corona from opposite directions. Thus, the data should appear as mirror images of each other. We report here on the results of the comparison of the images taken by the inner coronagraph (COR1) on the STEREO Ahead and Behind spacecraft in the hours when the separation was close to 180 degrees. We find that the intensity values seen by the two telescopes agree with each other to a high degree of accuracy. This validates both the radiometric intercalibration between the COR1 telescopes, and the method used to remove instrumental background from the images. The relative error between COR1-A and COR1-B is found to be less than 10(exp -9) B/B solar over most of the field-of-view, growing to a few x 10(exp -9) B/B solar for the brighter pixels near the edge of the occulter. The primary source of error is the background determination. We also report on the analysis of star observations which show that the absolute radiometric calibration of either COR1 telescope has not changed significantly since launch.

Thompson, W. T.↗
NASA NTRS2011

STEREO SECCHI COR1-A/B Intercalibration at 180 deg Separation

The twin Solar Terrestrial Relations Observatory (STEREO) spacecraft reached a separation angle of 180 deg on 6 February 2011. This provided a unique opportunity to test the intercalibration between the Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) telescopes on both spacecraft for areas above the limb. So long as the corona is optically thin, at 180 deg separation each spacecraft sees the same corona from opposite directions. Thus, the data should appear as mirror images of each other. We report here on the results of the comparison of the images taken by the inner coronagraph (COR1) on the STEREO-Ahead and -Behind spacecraft in the hours when the separation was close to 180 deg. We find that the intensity values seen by the two telescopes agree with each other to a high degree of accuracy. This validates both the radiometric intercalibration between the COR1 telescopes, and the method used to remove instrumental background from the images. The relative error between COR1-A and COR1-B is found to be less than 10-9 B/B over most of the field-of-view, growing to a few 10-9 B/B for the brighter pixels near the edge of the occulter. The primary source of error is the background determination. We also report on the analysis of star observations which show that the absolute radiometric calibration of either COR1 telescope has not changed significantly since launch.

Thompson, W. T.↗
NASA NTRS2012

Impacts of Assimilating MLS Temperature on the Upper Stratosphere in GEOS-5

Standard configurations of the GEOS-5 data assimilation system use nadir infrared and microwave sounders that provide deep-layer constraints on the thermal structure in the stratosphere. In the upper stratosphere, this information is currently provided by the Advanced Microwave Sounding Units (AMSU-As) on NOAA s polar-orbiting satellites. The highest peaking AMSU-A channel (14) peaks near 2.5hPa. Evaluation of the upper stratosphere reveals substantial biases in the temperature, cased in part by biases in the underlying GCM, and difficulties in representing the stratopause structure under disturbed conditions. This work demonstrates, unsurprisingly, that the assimilation into GEOS-5 of temperature profiles derived from EOS-Aura MLS leads to a substantially better representation of the stratopause structure from a climatological perspective and for disturbed events. Future plans with GEOS-5 include a reanalysis that includes numerous "research" datasets alongside the operational NOAA datasets that were used in MERRA. As preparation for this reanalysis, the present study examines how assimilating the MLS observations impact the error statistics for the AMSU-A instruments. Discussion will address the issue of bias correction for the AMSU-A Channel 14 radiances, which is presently turned off in GEOS-5 because of the absence of accurate temperature observations that can anchor the GEOS-5 analyses. The issue of what can be done in periods when no limb-sounder data are available will also be addressed.

Pawson, S.↗
NASA NTRS2014

Ozone Profiles in the Baltimore-Washington Region (2006-2011): Satellite Comparisons and DISCOVER-AQ Observations

Much progress has been made in creating satellite products for tracking the pollutants ozone and NO2 in the troposphere. Yet, in mid-latitude regions where meteorological interactions with pollutants are complex, accuracy can be difficult to achieve, largely due to persistent layering of some constituents. We characterize the layering of ozone soundings and related species measured from aircraft over two ground sites in suburban Washington, DC (Beltsville, MD, 39.05N; 76.9W) and Baltimore (Edgewood, MD, 39.4N; 76.3W) during the July 2011 DISCOVER-AQ (Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality) experiment. First, we compare column-ozone amounts from the Beltsville and Edgewood sondes with data from overpassing satellites. Second, processes influencing ozone profile structure are analyzed using Laminar Identification and tracers: sonde water vapor, aircraft CO and NOy. Third, Beltsville ozone profiles and meteorological influences in July 2011 are compared to those from the summers of 2006-2010. Sonde-satellite offsets in total ozone during July 2011 at Edgewood and Beltsville, compared to the Ozone Monitoring Instrument (OMI), were 3 percent mean absolute error, not statistically significant. The disagreement between an OMIMicrowave Limb Sounder-based tropospheric ozone column and the sonde averaged 10 percent at both sites, with the sonde usually greater than the satellite. Laminar Identification (LID), that distinguishes ozone segments influenced by convective and advective transport, reveals that on days when both stations launched ozonesondes, vertical mixing was stronger at Edgewood. Approximately half the lower free troposphere sonde profiles have very dry laminae, with coincident aircraft spirals displaying low CO (80-110 ppbv), suggesting stratospheric influence. Ozone budgets at Beltsville in July 2011, determined with LID, as well as standard meteorological indicators, resemble those of 4 of the previous 5 summers. The penetration of stratospheric air throughout the troposphere appears to be typical for summer conditions in the Baltimore-Washington region.

satellite validation↗
NASA NTRS2013

Ground-Based Lidar for Atmospheric Boundary Layer Ozone Measurements

Ground-based lidars are suitable for long-term ozone monitoring as a complement to satellite and ozonesonde measurements. However, current ground-based lidars are unable to consistently measure ozone below 500 m above ground level (AGL) due to both engineering issues and high retrieval sensitivity to various measurement errors. In this paper, we present our instrument design, retrieval techniques, and preliminary results that focus on the high-temporal profiling of ozone within the atmospheric boundary layer (ABL) achieved by the addition of an inexpensive and compact mini-receiver to the previous system. For the first time, to the best of our knowledge, the lowest, consistently achievable observation height has been extended down to 125 m AGL for a ground-based ozone lidar system. Both the analysis and preliminary measurements demonstrate that this lidar measures ozone with a precision generally better than 10% at a temporal resolution of 10 min and a vertical resolution from 150 m at the bottom of the ABL to 550 m at the top. A measurement example from summertime shows that inhomogeneous ozone aloft was affected by both surface emissions and the evolution of ABL structures.

differential absorption lidar↗
NASA NTRS2010

SIM-Lite Mission Spectral Calibration Sensitivities and Refinements

SIM-Lite missions will perform astrometry at microarcsecond accuracy using star light interferometry. For typical baselines that are shorter than 10 meters, this requires to measure optical path difference (OPD) accurate to tens of picometers calling for highly accurate calibration. A major challenge is to calibrate the star spectral dependency in fringe measurements -- the spectral calibration. Previously, we have developed a spectral calibration and estimation scheme achieving picometer level accuracy. In this paper, we present the improvements regarding the application of this scheme from sensitivity studies. Data from the SIM Spectral Calibration Development Unit (SCDU) test facility shows that the fringe OPD is very sensitive to pointings of both beams from the two arms of the interferometer. This sensitivity coupled with a systematic pointing error provides a mechanism to explain the bias changes in 2007. Improving system alignment can effectively reduce this sensitivity and thus errors due to pointing errors. Modeling this sensitivity can lead to further improvement in data processing. We then investigate the sensitivity to a model parameter, the bandwidth used in the fringe model, which presents an interesting trade between systematic and random errors. Finally we show the mitigation of calibration errors due to system drifts by interpolating instrument calibrations. These improvements enable us to use SCDU data to demonstrate that SIM-Lite missions can meet the 1pm noise floor requirement for detecting earth-like exoplanets.

wave front aberration↗
NASA NTRS2019

Gravitational Changes of the Earth's Free Oscillation From Earthquakes: Theory and Feasibility Study Using GRACE Inter‐Satellite Tracking

GRACE satellites have detected regional‐scale preseismic, coseismic, and postseismic gravity changes associated with great earthquakes during the GRACE era (2002‐2017). Earthquakes also excite global‐scale transient gravity changes associated with free oscillations that may be discerned for a few days. In this study, we examine such global gravity changes due to Earth's free oscillations and quantify how they affect GRACE measurements. We employ the normal mode formalism to synthesize the global gravity changes after the 2004 Sumatra earthquake and simulate the (gravitational) free oscillation signals manifested in the GRACE K‐band ranging (KBR) measurements. Using the Kaula orbit perturbation theory, we show how GRACE inter‐satellite distances are perturbed through a complex coupling of eigenfrequencies of the normal modes with the Earth's rotation rate and the GRACE satellites' orbital frequency. It is found that a few gravest normal modes can generate range‐rate perturbations as large as 0.2 μm/s, which are comparable to actual errors of GRACE KBR ranging and accelerometer instruments. Wavelet time‐frequency analysis of the GRACE KBR residual data in December 2004 reveals the existence of a significant transient signal after the 2004 Sumatra earthquake. This transient signal is characterized by a frequency of ~0.022 mHz that could be potentially associated with the largest excitation due to the “football” mode of the Earth's free oscillation. However, the results are also affected by low‐frequency noise of the GRACE accelerometers. Improved space‐borne gravitational instrumentation may open new opportunities to study the Earth's interior and earthquakes independently from global seismological analysis.

Ghobadi-Far, Khosro↗
NASA NTRS2018

KaRIn Alignment Mechanism Design, Development, and Testing

The Ka-Band Radar Interferometric System (KaRIn) will characterize the ocean mesoscale/submesoscale circulation and provide a global inventory of all lakes, reservoirs, wetlands, and major rivers. There are two identical Alignment Mechanisms (AM) mirrored on the instrument to correct KaRIn Azimuth radar pointing errors. Each AM is a one-degree-of-freedom precision mechanism. The mechanism must meet challenging thermoelastic distortion requirements over a wide temperature range. The flight design was qualified in less than two years, and the flight hardware is currently in acceptance testing. Discussed are key design details along with supporting development and qualification test results.

Wolff, John Luke↗
NASA NTRS1991

Spatial sampling errors for a satellite-borne scanning radiometer

The Clouds and Earth's Radiant Energy System (CERES) scanning radiometer is planned as the Earth radiation budget instrument for the Earth Observation System, to be flown in the late 1990's. In order to minimize the spatial sampling errors of the measurements, it is necessary to select design parameters for the instrument such that the resulting point spread function will minimize spatial sampling errors. These errors are described as aliasing and blurring errors. Aliasing errors are due to presence in the measurements of spatial frequencies beyond the Nyquist frequency, and blurring errors are due to attenuation of frequencies below the Nyquist frequency. The design parameters include pixel shape and dimensions, sampling rate, scan period, and time constants of the measurements. For a satellite-borne scanning radiometer, the pixel footprint grows quickly at large nadir angles. The aliasing errors thus decrease with increasing scan angle, but the blurring errors grow quickly. The best design minimizes the sum of these two errors over a range of scan angles. Results of a parameter study are presented, showing effects of data rates, pixel dimensions, spacecraft altitude, and distance from the spacecraft track.

Manalo, Natividad D.↗
NASA NTRS2007

The NIRCam Optical Telescope Simulator (NOTES)

The Near Infra-Red Camera (NIRCam), the 0.6-5.0 micron imager and wavefront sensing instrument for the James Webb Space Telescope (JWST), will be used on orbit both as a science instrument, and to tune the alignment of the telescope. The NIRCam Optical Telescope Element Simulator (NOTES) will be used during ground testing to provide an external stimulus to verify wavefront error, imaging characteristics, and wavefront sensing performance of this crucial instrument. NOTES is being designed and built by NASA Goddard Space Flight Center with the help of Swales Aerospace and Orbital Sciences Corporation. It is a single-point imaging system that uses an elliptical mirror to form an U20 image of a point source. The point source will be fed via optical fibers from outside the vacuum chamber. A tip/tilt mirror is used to change the chief ray angle of the beam as it passes through the aperture stop and thus steer the image over NIRCam's field of view without moving the pupil or introducing field aberrations. Interchangeable aperture stop elements allow us to simulate perfect JWST wavefronts for wavefront error testing, or introduce transmissive phase plates to simulate a misaligned JWST segmented mirror for wavefront sensing verification. NOTES will be maintained at an operating temperature of 80K during testing using thermal switches, allowing it to operate within the same test chamber as the NIRCam instrument. We discuss NOTES' current design status and on-going development activities.

Kubalak, David↗
NASA NTRS1924

A Method for the Instantaneous Determination of the Velocity and Direction of the Wind

The laboratory instruments, which we often constructed with makeshift means, gave encouraging results and showed that they could satisfactorily meet the required conditions. By limiting ourselves to the employment of hot wires of 0.05 mm (0.002 in.) diameter, we obtained instruments which faithfully followed all the wind fluctuations of over 0.1 second and even much more rapid variations without any very great error.

INSTRUMENTS - ANEMOMETERS↗