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NASA NTRS1992

Supervised fully polarimetric classification of the Black Forest test site: From MAESTROI to MAC Europe

A study on the performance of a supervised fully polarimetric maximum likelihood classifier for synthetic aperture radar (SAR) data when applied to a specific classification context: forest classification based on age classes and in the presence of a sloping terrain is presented. For the experimental part, the polarimetric AIRSAR data at P, L, and C-band, acquired over the German Black Forest near Freiburg in the frame of the 1989 MAESTRO-1 campaign and the 1991 MAC Europe campaign was used, MAESTRO-1 with an ESA/JRC sponsored campaign, and MAC Europe (Multi-sensor Aircraft Campaign); in both cases the multi-frequency polarimetric JPL Airborne Synthetic Aperture Radar (AIRSAR) radar was flown over a number of European test sites. The study is structured as follows. At first, the general characteristics of the classifier and the dependencies from some parameters, like frequency bands, feature vector, calibration, using test areas lying on a flat terrain are investigated. Once it is determined the optimal conditions for the classifier performance, we then move on to the study of the slope effect. The bulk of this work is performed using the Maestrol data set. Next the classifier performance with the MAC Europe data is considered. The study is divided into two stages: first some of the tests done on the Maestro data are repeated, to highlight the improvements due to the new processing scheme that delivers 16 look data. Second we experiment with multi images classification with two goals: to assess the possibility of using a training set measured from one image to classify areas in different images; and to classify areas on critical slopes using different viewing angles. The main points of the study are listed and some of the results obtained so far are highlighted.

Degrandi, G.↗

NASA NTRS2016

Hyperspectral Cubesat Constellation for Natural Hazard Response

The authors on this paper are team members of the Earth Observing 1 (E0-1) mission which has flown an imaging spectrometer (hyperspectral) instrument called Hyperion for the past 15+ years. The satellite is able to image any spot on Earth in the nadir looking direction every 16 days and with slewing, of the satellite for up to a 23 degree view angle, any spot on the Earth can be imaged approximately every 2 to 3 days. EO-1 has been used to track many natural hazards such as wildfires, volcanoes and floods. An enhanced capability that has been sought is the ability to image natural hazards in a daily time series for space-based imaging spectrometers. The Hyperion cannot provide this capability on EO-1 with the present polar orbit. However, a constellation of cubesats, each with the same imaging spectrometer, positioned strategically can be used to provide daily coverage or even diurnal coverage, cost-effectively. This paper sought to design a cubesat constellation mission that would accomplish this goal and then to articulate the key tradeoffs.

Onboarding process↗

NASA NTRS2016

Impact of Spatial Sampling on Continuity of MODIS-VIIRS Land Surface Reflectance Products: A Simulation Approach

With the increasing need to construct long-term climate-quality data records to understand, monitor, and predict climate variability and change, it is vital to continue systematic satellite measurements along with the development of new technology for more quantitative and accurate observations. The Suomi National Polar-orbiting Partnership mission provides continuity in monitoring the Earths surface and its atmosphere in a similar fashion as the heritage MODIS instruments onboard the National Aeronautics and Space Administrations Terra and Aqua satellites. In this paper, we aim at quantifying the consistency of Aqua MODIS and Suomi-NPP Visible Infrared Imaging Radiometer Suite (VIIRS) Land Surface Reflectance (LSR) and NDVI products as related to their inherent spatial sampling characteristics. To avoid interferences from sources of measurement and/or processing errors other than spatial sampling, including calibration, atmospheric correction, and the effects of the bidirectional reflectance distribution function, the MODIS and VIIRSLSR products were simulated using the Landsat-8s Operational Land Imager (OLI) LSR products. The simulations were performed using the instruments point spread functions on a daily basis for various OLI scenes over a 16-day orbit cycle. It was found that the daily mean differences due to discrepancies in spatial sampling remain below 0.0015 (1) in absolute surface reflectance at subgranule scale (i.e., OLI scene size).We also found that the MODISVIIRS product intercomparisons appear to be minimally impacted when differences in the corresponding view zenith angles (VZAs) are within the range of -15deg to -35deg (VZA(sub v) - VZA(sub m)), where VIIRS and MODIS footprints resemble in size. In general, depending on the spatial heterogeneity of the OLI scene contents, per-grid-cell differences can reach up to 20.Further spatial analysis of the simulated NDVI and LSR products revealed that, depending on the user accuracy requirements for product intercomparisons, spatial aggregations may be used. It was found that if per-grid-cell differences on the order of 10(in LSR or NDVI) are tolerated, the product intercomparisons are expected to be immune from differences in spatial sampling.

VIIRS↗

NASA NTRS2018

Results from the Deep Convective Clouds-Based Response Versus Scan-Angle Characterization for the MODIS Reflective Solar Bands

The Terra and Aqua Moderate-Resolution Imaging Spectroradiometer (MODIS) scan mirror reflectance is a function of the angle of incidence (AOI) and was characterized prior to launch by the instrument vendor. The relative change of the prelaunch response versus scan angle (RVS) is tracked and linearly scaled on-orbit using observations at two AOIs of 11.2° and 50.2° corresponding to the moon view and solar diffuser, respectively. As the missions continue to operate well beyond their design life of six years, the assumption of linear scaling between the two AOIs is known to be inadequate in accurately characterizing the RVS, particularly at short wavelengths. Consequently, an enhanced approach of supplementing the on-board measurements with response trends from desert pseudoinvariant calibration sites (PICS) was formulated in MODIS Collection 6 (C6). An underlying assumption for the continued effectiveness of this approach is the long-term (multiyear) and short-term (month to month) stability of the PICS. Previous work has shown that the deep convective clouds (DCC) can also be used to monitor the onorbit RVS performance with less trend uncertainties compared with desert sites. In this paper, the raw sensor response to the DCC is used to characterize the on-orbit RVS on a band and mirror-side basis. These DCC-based RVS results are compared with those of C6 PICS-based RVS, showing an agreement within 2% observed in most cases. The pros and cons of using a DCC-based RVS approach are also discussed in this paper. Although this reaffirms the efficacy of the C6 PICS-based RVS, the DCC-based RVS approach presents itself as an effective alternative for future considerations. Potential applications of this approach to other instruments, such as Suomi National Polarorbiting Partnership, Joint Polar Satellite Systems, and Visible Infrared Imaging Radiometer Suite, are also discussed.

Angal, Amit↗

NASA NTRS2020

Photometry of Asteroid (101955) Bennu with OVIRS on OSIRIS-REx

NASA’s OSIRIS-REx spacecraft arrived at its sampling target, asteroid (101955) Bennu, in December 2018 and started a series of global observation campaigns. Here we investigate the global photometric properties of Bennu as observed by the OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS) over the time period December 9, 2018, to September 26, 2019. In this study we used observations obtained over wavelengths ranging from 0.4 to 3.7 μm, with a solar phase angle range of 5.3° to 132.6°. Our aim is to characterize the global average disk-resolved photometric properties of Bennu with multiple models. The best-fit model is a McEwen model with an exponential phase function and an exponential polynomial partition function. We use this model to correct the OVIRS spectra of Bennu to a standard reference viewing and illumination geometry at visible to infrared wavelengths for the purposes of global spectral mapping. We derive a bolometric Bond albedo map in which Bennu’s surface values range from 0.021 to 0.027. We find a phase reddening effect, and our model is effective at removing this phase reddening. Our average model albedo shows a blueish spectrum with a >10% absorption feature centered at 2.74 μm. Of all comparisons with previously visited asteroids and comets, only 28P/Neujmin, 2P/Encke, and (162173) Ryugu are darker than Bennu. We find that Bennu is a few percent brighter than Ryugu in the wavelengths respectively observed by the OSIRIS-REx and Hayabusa2 missions (from 0.48 to 0.86 μm). We also compare our spectroscopic photometry of Bennu with the OSIRIS-REx imaging photometry and with ground-based predictions.

Asteroid Bennu↗

NASA NTRS1982

Sigma/deg/ signature of the Amazon rain forest obtained from the Seasat scatterometer

Scatterometer data from Seasat of the Amazon rain forest were examined to determine if the region is suitable to use as a reference for calibration of radars. The consistency of Skylab data viewing the Amazon region prompted the analyses, and the Seasat-A scatterometer system (SASS) gathered data of the same region at varying angles. The instrument employed a 100 W 14.6 GHz signal with the reflected power sampled 61 times during each 1.89 sec measurement period. Doppler filters were used in 15 parallel channels of reception, and represented areas 20 km by 50-70 km. Tests were made of regional and temporal stability of the Amazon area, with five measurement angles averaged at different incidence angles to find the mean deviation, which was found to be less than 0.5 dB. Diurnal effects were confined to early morning, and further tests are recommended to obtain results for an entire year, to develop screening methods for thick clouds and rain, and to determine the deviation more precisely.

Birrer, I. J.↗

NASA NTRS1984

Magnetic field draping against the dayside magnetopause

Interplanetary magnetic fields observed upstream of Earth's magnetosphere at ISEE 3 form input for a gasdynamic model of magnetic field draping in the dayside magnetosheath. Model results near the magnetopause are compared with appropriately lagged observations at ISEE 1. In 16 to 24 cases, the angle between the transverse component of the model and observed fields is less than 20 deg. The agreement is surprisingly good in view of the uncertainty introduced by the large distances between ISEE 1 and ISEE 3. The results indicate that magnetohydrodynamic and energy transfer processes at the magnetopause do not cause large distortions of the magnetosheath magnetic field. In addition, a comparison between observed and model field magnitudes indicates that immediately outside the magnetopause the observed field behaves like the model field at a distance of approx. 0.5 R sub E from the magnetopause, outside the region where magnetohydrodynamic effects make the gasdynamic model inapplicable. Patterns of model magnetic field orientation at the magnetopause are presented for practical application.

Crooker, N. U.↗

NASA NTRS1985

Magnetic field draping against the dayside magnetopause

Interplanetary magnetic fields observed upstream of earth's magnetosphere at ISEE 3 form input for a gasdynamic model of magnetic field draping in the dayside magnetosheath. Model results near the magnetopause are compared with appropriately lagged observations at ISEE 1. In 16 to 24 cases, the angle between the transverse component of the model and observed fields is less than 20 deg. The agreement is surprisingly good in view of the uncertainty introduced by the large distances between ISEE 1 and ISEE 3. The results indicate that magnetohydrodynamic and energy transfer processes at the magnetopause do not cause large distortions of the magnetosheath magnetic field. In addition, a comparison between observed and model field magnitudes indicates that immediately outside the magnetopause the observed field behaves like the model field at a distance of approx. 0.5 R sub E from the magnetopause, outside the region where magnetohydrodynamic effects make the gasdynamic model inapplicable. Patterns of model magnetic field orientation at the magnetopause are presented for practical application.

Crooker, N. U.↗

NASA NTRS2004

Limitation of Liquid Crystal on Silicon Spatial Light Modular for Holographic Three-dimensional Displays

In a 3-D display system based on an opto-electronic reconstruction of a digitally recorded hologram, the field of view of such a system is limited by the spatial resolution of the liquid crystal on silicon (LCOS) spatial light modular (SLM) used to perform the opto-electronic reconstruction. In this article, the special resolution limitation of LCOS SLM associated with the fringe field effect and interpixel coupling is determined by the liquid crystal detector simulation and the Finite Difference Time Domain (FDTD) simulation. The diffraction efficiency loss associated with the imperfection in the phase profile is studied with an example of opto-electronic reconstruction of an amplitude object. A high spatial resolution LCOS SLM with a wide reconstruction angle is proposed.

Wang, Xinghua↗

NASA NTRS2023

Characterization of Slat Noise Radiation from a High-Lift Common Research Model

A test campaign was conducted in the open-jet test section of the NASA Langley 14- by 22-Foot Subsonic Tunnel on a 10%-scale, semispan version of a High-Lift Common Research Model (CRM-HL) incorporating a leading-edge slat, trailing-edge flap and removable high-fidelity main landing gear. Aerodynamic and far field acoustic measurements were obtained on baseline and acoustically treated model configurations using an ensemble of time-averaged and unsteady surface pressure sensors paired with a traversing 97-microphone phased array viewing the pressure side of the airframe. A modified version of the DAMAS deconvolution method incorporating corrections for shear layer acoustic wave decorrelation was employed to determine the locations and strengths of relevant noise sources along the span of the slat and in the vicinity of the flap edges and landing gear. The main goal of the test campaign was to use the surface pressure and array data to evaluate the effectiveness of various slat noise reduction concepts. It was found that slat-gap fillers produced significant broadband noise reduction with minimal aerodynamic performance penalties for all Mach numbers and airfoil angles of attack that were investigated. The test campaign clearly demonstrated the noise reduction benefits that can be obtained by applying appropriate treatments to leading-edge slats on commercial transport-class aircraft.

Aeronautics Research Mission Directorate↗

NASA NTRS2020

Performance Assessments of the SNPP and N20 VIIRS DNB Using Observations of Bright Stars

The Visible Infrared Imaging Radiometer Suite (VIIRS) on-board the Suomi-NPP (SNPP) and NOAA-20 (N20) spacecrafts is a multi-spectral Earth-observing instrument with spectral channels ranging from the visible to the long-wave infrared. In addition to these spectral channels, the VIIRS instrument features a panchromatic Day/Night band (DNB) with 3 gain stages (low, mid, and high) which allows for Earth-view (EV) radiance retrievals over 7 orders of magnitude. The DNB is able to collect data ranging from dim city lights during nighttime up to reflected sunlight from cloud-tops during daytime. The DNB data collection is divided into 32 aggregation modes, where sub-pixel aggregation is used to maintain a nearly constant pixel footprint on ground during EV data collection throughout each scan. The DNB is also sensitive enough to observe bright stars through the instrument space-view (SV) port. Data from these bright stars can be used to track the temporal stability of the sensor gain and as a method of intercomparison between the two VIIRS instruments. In this work, we will present several sensor performance assessments of the VIIRS DNB using stars. In addition to the sensor gain trending, these assessments will include a comparison of the differences between the daytime and nighttime data due to the effects of stray-light, a comparison of the measured signal as a function of aggregation mode, a comparison between the two high-gain sub-stages, and half-angle mirror side for both the SNPP and N20 VIIRS DNB.

VIIRS↗

NASA NTRS2017

Bitcoin, Blockchains and Efficient Distributed Spacecraft Mission Control

Earth Observing 1 (E0-1) satellite has an imaging spectrometer (hyperspectral) instrument called Hyperion. The satellite is able to image any spot on Earth in the nadir looking direction every 16 days. With slewing of the satellite and allowing for up to a 23 degree view angle, any spot on the Earth can be imaged approximately every 2 to 3 days. EO-1 has been used to track many natural hazards such as wildfires, volcanoes and floods. An enhanced capability that is sought is the ability to image natural hazards in a daily time series for space based imaging spectrometers. The Hyperion can not provide this capability on EO-1 with the present polar orbit. However, a constellation of cubesats each powered with Intelligent Payload Modules, and each with copies of a commercial imaging spectrometer, positioned strategically in the same orbit, can be used to provide daily coverage, cost-effectively.

Blockchain in spac↗

NASA NTRS2015

Hyperspectral Cubesat Constellation for Natural Hazard Response (Follow-On)

Onboard Processing↗

NASA NTRS1994

Multiple View Zenith Angle Observations of Reflectance From Ponderosa Pine Stands

Reflectance factors (RF(lambda)) from dense and sparse ponderosa pine (Pinus ponderosa) stands, derived from radiance data collected in the solar principal plane by the Advanced Solid-State Array Spectro-radiometer (ASAS), were examined as a function of view zenith angle (theta(sub v)). RF(lambda) was maximized with theta(sub v) nearest the solar retrodirection, and minimized near the specular direction throughout the ASAS spectral region. The dense stand had much higher RF anisotropy (ma)dmurn RF is minimum RF) in the red region than did the sparse stand (relative differences of 5.3 vs. 2.75, respectively), as a function of theta(sub v), due to the shadow component in the canopy. Anisotropy in the near-infrared (NIR) was more similar between the two stands (2.5 in the dense stand and 2.25 in the sparse stand); the dense stand exhibited a greater hotspot effect than 20 the sparse stand in this spectral region. Two common vegetation transforms, the NIR/red ratio and the normalized difference vegetation index (NDVI), both showed a theta(sub v) dependence for the dense stand. Minimum values occurred near the retrodirection and maximum values occurred near the specular direction. Greater relative differences were noted for the NIR/red ratio (2.1) than for the NDVI (1.3). The sparse stand showed no obvious dependence on theta(sub v) for either transform, except for slightly elevated values toward the specular direction.

Johnson, Lee F.↗

NASA NTRS1995

Evaluation of restraint system concepts for the Japanese Experiment Module flight demonstration

The current International Space Station configuration includes a Japanese Experiment Module which relies on a large manipulator and a smaller dexterous manipulator to operate outside the pressurized environment of the experiment module. The module's flight demonstration is a payload that will be mounted in the aft flight deck on STS-87 to evaluate a prototype of the dexterous manipulator. Since the payload operations entail two 8-hour scenarios on consecutive days, adequate operator restraint at the workstation will be critical to the perceived success or failure of the payload. Simulations in reduced gravity environment on the KC-135A were the only way to evaluate the restraint systems and workstation configuration. Two astronaut and two non-astronaut operators evaluated the Advanced Lower Body Extremities Restraint Test and a foot loop restraint system by performing representative tasks at the workstation in each of the two restraint systems; at the end of each flight they gave their impressions of each system and the workstation. Results indicated that access to the workstation switch panels was difficult and manipulation of the hand controllers forced operators too low for optimal viewing of the aft flight deck monitors. The workstation panel should be angled for better visibility, and infrequently used switches should be on the aft flight deck panel. Pitch angle and placement of the hand controllers should optimize the operator's eye position with respect to the monitors. The lower body restraint was preferred over the foot loops because it allowed operators to maintain a more relaxed posture during long-duration tasks, its height adjustability allowed better viewing of aft flight deck monitors, and it provided better restraint for reacting forces imparted on the operator at the workstation. The foot loops provide adequate restraint for the flight demonstration tasks identified. Since results will impact the design of the workstation, both restraints should be flown and used during operation of the flight demonstration payload to evaluate the effect of restraint during long-duration tasks.

Sampaio, Carlos E.↗

NASA NTRS2003

Daytime adaptive optics for deep space optical communications

The deep space optical communications subsystem offers a higher bandwidth communications link in smaller size, lower mass, and lower power consumption subsystem than does RF. To demonstrate the benefit of this technology to deep space communications NASA plans to launch an optical telecommunications package on the 2009 Mars Telecommunications orbiter spacecraft. Current performance goals are 30-Mbps from opposition, and 1-Mbps near conjunction (-3 degrees Sun-Earth-Probe angle). Yet, near conjunction the background noise from the day sky will degrade the performance of the optical link. Spectral and spatial filtering and higher modulation formats can mitigate the effects of background sky. Narrowband spectral filters can result in loss of link margin, and higher modulation formats require higher transmitted peak powers. In contrast, spatial filtering at the receiver has the potential of being lossless while providing the required sky background rejection. Adaptive optics techniques can correct wave front aberrations caused by atmospheric turbulence and enable near-diffraction-limited performance of the receiving telescope. Such performance facilitates spatial filtering, and allows the receiver field-of-view and hence the noise from the sky background to be reduced.

adaptive optics↗

NASA NTRS2018

Preliminary Study of JPSS-1/NOAA-20 VIIRS Day-Night Band Straylight Characterization and Correction Methods

The JPSS-1 (now named NOAA-20) VIIRS instrument has successfully operated since its launch in November 18, 2017. A panchromatic channel onboard NOAA-20 VIIRS is called the day-night band (DNB). With its large dynamic range and high sensitivity, the DNB detectors can make observations during both daytime and nighttime. However, the DNB night image quality is affected by the straylight contamination. In this study, we focused on Earth view data in the midto-high latitude of the northern and southern hemispheres when spacecraft is crossing the day/night terminators at the beginning of NOAA-20 mission. Based on on-orbit data analysis from previous VIIRS sensor onboard S-NPP mission, straylight contamination mainly depends on the Earth-Sun-spacecraft geometry, and it is also detector and scan-angle dependent. Inter-comparison investigation of straylight behavior in both SNPP and NOAA-20 instruments will be conducted to better understand straylight characteristics. The preliminary study has been performed in this paper to mitigate straylight contamination for NOAA-20VIIRS DNB night images. The effectiveness of the straylight correction algorithm, directly adapted from the S-NPP DNB, is assessed for night images in the day/night terminators. Further work has been identified to improve current straylight correction methodology and DNB-based environmental data products.NOAA-20.

Day-Night Band↗

NASA NTRSDate not supplied

Radiative Flux Measurements from ARISE: A Comparison with CERES Top-of-Atmosphere Radiative Fluxes

Uncertainty in top-of-atmosphere (TOA) radiation fluxes observations are larger in the Arctic than in other regions. These uncertainties are due to the low sun angles and the highly reflective, anisotropic, and heterogeneous surface conditions. Quantifying, attributing, and reducing Arctic TOA radiative flux uncertainty enables a better understanding of the rapidly changing Arctic. To advance this goal, we compare the Cloud and Earth’s Radiant Energy System (CERES) TOA radiative fluxes with Arctic Radiation-IceBridge Sea and Ice Experiment (ARISE) campaign measurements collected in September 2014. We compare CERES TOA and aircraft radiative flux measurements using two complementary approaches: grid box average fluxes and instantaneously matched footprints. The grid box mean flux comparison indicates an agreement between CERES and aircraft measurements within 2 uncertainty (calibration and inversion) in the longwave for all five grid boxes and for four-of-five grid boxes in the shortwave; shortwave and longwave mean differences are -7.9 and +2.3 Wm‑2, respectively. The comparison of 36 instantaneously matched footprints with aircraft measurements reveals mean differences of -10.5 and 0.4 Wm‑2 in the shortwave and longwave, respectively. To further explore the persistent negative difference in the shortwave, we further quantify the effects of temporal and spatial sampling differences, angular distribution models, and scene identification to CERES-aircraft differences. Our analysis indicates that sampling differences (including scene evolution) account for an additional 1.8 and 1.7% uncertainty in the shortwave and longwave, respectively and indicates no bias. After accounting for this sampling uncertainty, all CERES-aircraft grid box mean fluxes agree within 2 uncertainty. Scene identification errors due to sea ice concentration data set differences exhibit no bias in the shortwave flux difference and indicate the possibility of substantial differences in the CERES fluxes in specific cases with large spatial heterogeneity. Considering the instantaneously matched footprints, we find that the angular distribution models account may account for up to ‑7.3 Wm-2 of the persistent CERES-aircraft shortwave flux difference due to systematic differences in the anisotropy for sea ice partly cloudy scenes. Additional analysis using a special scan model with the CERES FM2 instrument suggests a significant view zenith angle dependence of the CERES fluxes for sea ice partly cloudy scenes where shortwave fluxes systematically decrease with increasing view zenith angle; no dependence is found for other scene types. We conclude that (1) spatial heterogeneity and scene temporal evolution substantially limit our ability to use aircraft measurements to place strong constraints on CERES TOA fluxes and (2) that the representation of anisotropy in sea ice partly cloudy scenes is a significant factor contributing to the persistent negative CERES-aircraft shortwave flux difference in this comparison and require additional data to analysis fully quantify the potential bias.

Patrick C Taylor↗