National Aeronautics And Space Administration Langley Research Center Research Articles

Coupled Retrieval of Liquid Water Cloud and Above‐Cloud Aerosol Properties Using the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI)

AbstractAn optimization algorithm is developed to retrieve liquid water cloud properties including cloud optical depth (COD), droplet size distribution and cloud top height (CTH), and above‐cloud aerosol properties including aerosol optical depth (AOD), single‐scattering albedo, and microphysical properties from sweep‐mode observations by Jet Propulsion Laboratory's Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) instrument. The retrieval is composed of three major steps: (1) initial estimate of the mean droplet size distribution across the entire image of 80–100 km along track by 10–25 km across track from polarimetric cloudbow observations, (2) coupled retrieval of image‐scale cloud and above‐cloud aerosol properties by fitting the polarimetric data at all observation angles, and (3) iterative retrieval of 1‐D radiative transfer‐based COD and droplet size distribution at pixel scale (25 m) by establishing relationships between COD and droplet size and fitting the total radiance measurements. Our retrieval is tested using 134 AirMSPI data sets acquired during the National Aeronautics and Space Administration (NASA) field campaign ObseRvations of Aerosols above CLouds and their intEractionS. The retrieved above‐cloud AOD and CTH are compared to coincident HSRL‐2 (HSRL‐2, NASA Langley Research Center) data, and COD and droplet size distribution parameters (effective radius reff and effective variance veff) are compared to coincident Research Scanning Polarimeter (RSP) (NASA Goddard Institute for Space Studies) data. Mean absolute differences between AirMSPI and HSRL‐2 retrievals of above‐cloud AOD at 532 nm and CTH are 0.03 and <0.5 km, respectively. At RSP's footprint scale (~ 323 m), mean absolute differences between RSP and AirMSPI retrievals of COD, reff, and veff in the cloudbow area are 2.33, 0.69 μm, and 0.020, respectively. Neglect of smoke aerosols above cloud leads to an underestimate of image‐averaged COD by ~15%.

Arctic Radiation-IceBridge Sea and Ice Experiment: The Arctic Radiant Energy System during the Critical Seasonal Ice Transition

Abstract The National Aeronautics and Space Administration (NASA)’s Arctic Radiation-IceBridge Sea and Ice Experiment (ARISE) acquired unique aircraft data on atmospheric radiation and sea ice properties during the critical late summer to autumn sea ice minimum and commencement of refreezing. The C-130 aircraft flew 15 missions over the Beaufort Sea between 4 and 24 September 2014. ARISE deployed a shortwave and longwave broadband radiometer (BBR) system from the Naval Research Laboratory; a Solar Spectral Flux Radiometer (SSFR) from the University of Colorado Boulder; the Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) from the NASA Ames Research Center; cloud microprobes from the NASA Langley Research Center; and the Land, Vegetation and Ice Sensor (LVIS) laser altimeter system from the NASA Goddard Space Flight Center. These instruments sampled the radiant energy exchange between clouds and a variety of sea ice scenarios, including prior to and after refreezing began. The most critical and unique aspect of ARISE mission planning was to coordinate the flight tracks with NASA Cloud and the Earth’s Radiant Energy System (CERES) satellite sensor observations in such a way that satellite sensor angular dependence models and derived top-of-atmosphere fluxes could be validated against the aircraft data over large gridbox domains of order 100–200 km. This was accomplished over open ocean, over the marginal ice zone (MIZ), and over a region of heavy sea ice concentration, in cloudy and clear skies. ARISE data will be valuable to the community for providing better interpretation of satellite energy budget measurements in the Arctic and for process studies involving ice–cloud–atmosphere energy exchange during the sea ice transition period.

Results from the NASA GSFC and LaRC Ozone Lidar Intercomparison: New Mobile Tools for Atmospheric Research

AbstractDuring a 2-week period in May 2014, the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center Tropospheric Ozone Differential Absorption Lidar (GSFC TROPOZ DIAL) was situated near the NASA Langley Research Center (LaRC) Mobile Ozone Lidar (LMOL) and made simultaneous measurements for a continuous 15-h observation period in which six separate ozonesondes were launched to provide reference ozone profiles. Although each of these campaign-ready lidars has very different transmitter and receiver components, they produced very similar ozone profiles, which were mostly within 10% of each other and the ozonesondes. The observed column averages as compared to the ozonesondes also agree well and are within 8% of each other. A robust uncertainty analysis was performed, and the results indicate that there is no statistically significant systematic bias between the TROPOZ and LMOL instruments. With the extended measurements and ozonesonde launches, this intercomparison has yielded an in-depth evaluation of the precision and accuracy of the two new lidars. This intercomparison is also the first (to the best of the authors’ knowledge) reported measurement intercomparison of two ground-based tropospheric ozone lidar systems within the United States.

Silence of the drones: how to hush the humming

Drones tend to live up to their name, emitting a low buzz that may be a problem if fleets of delivery drones start operating in urban airspace. But a team from the National Aeronautics and Space Administration (NASA) has now developed a way to silence that annoying noise. The GL-10 is the latest in a series of prototypes from NASAs Langley Research Center in Hampton VA. It is made from carbon fibre and has a wingspan of 3 meters. But its most unusual feature is the large number of engine, with eight on the wings and another two on the tail. One aim at this is to generate efficient electric propulsion, but the project also solves the problem of aircraft noise: several small motors are quieter than a few large ones. The GL-10 uses Leading Edge Asynchronous Propeller technology, which prevents the sound from the propellers combining into one loud noise or harmonic.

Intercomparison of Water Vapor Data Measured with Lidar during IHOP_2002. Part I: Airborne to Ground-Based Lidar Systems and Comparisons with Chilled-Mirror Hygrometer Radiosondes

AbstractThe water vapor data measured with airborne and ground-based lidar systems during the International H2O Project (IHOP_2002), which took place in the Southern Great Plains during 13 May–25 June 2002 were investigated. So far, the data collected during IHOP_2002 provide the largest set of state-of-the-art water vapor lidar data measured in a field campaign. In this first of two companion papers, intercomparisons between the scanning Raman lidar (SRL) of the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) and two airborne systems are discussed. There are 9 intercomparisons possible between SRL and the differential absorption lidar (DIAL) of Deutsches Zentrum für Luft- und Raumfahrt (DLR), while there are 10 intercomparisons between SRL and the Lidar Atmospheric Sensing Experiment (LASE) of the NASA Langley Research Center. Mean biases of (−0.30 ± 0.25) g kg−1 or −4.3% ± 3.2% for SRL compared to DLR DIAL (DLR DIAL drier) and (0.16 ± 0.31) g kg−1 or 5.3% ± 5.1% for SRL compared to LASE (LASE wetter) in the height range of 1.3–3.8 km above sea level (450–2950 m above ground level at the SRL site) were found. Putting equal weight on the data reliability of the three instruments, these results yield relative bias values of −4.6%, −0.4%, and +5.0% for DLR DIAL, SRL, and LASE, respectively. Furthermore, measurements of the Snow White (SW) chilled-mirror hygrometer radiosonde were compared with lidar data. For the four comparisons possible between SW radiosondes and SRL, an overall bias of (−0.27 ± 0.30) g kg−1 or −3.2% ± 4.5% of SW compared to SRL (SW drier) again for 1.3–3.8 km above sea level was found. Because it is a challenging effort to reach an accuracy of humidity measurements down to the ∼5% level, the overall results are very satisfactory and confirm the high and stable performance of the instruments and the low noise errors of each profile.

Real-Time Implementation of Obstacle Detection Algorithms on a Datacube MaxPCI Architecture

The high-speed civil transport (HSCT) aircraft has been designed with limited cockpit visibility. To handle this, the National Aeronautics and Space Administration (NASA) has proposed an external visibility system (XVS) to aid pilots in overcoming this lack of visibility. XVS obtains video images using high-resolution cameras mounted on and directed outside the aircraft. Images captured by the XVS enable automatic computer analysis in real-time, and thereby alert pilots about potential flight path hazards. Thus, the system is useful in helping pilots avoid air collisions. In this study, a system was configured to capture image sequences from an on-board high-resolution digital camera at a live video rate, record the images into a high-speed disk array through a fiber channel, and process the images using a Datacube MaxPCI machine with multiple pipelined processors to perform real-time obstacle detection. In this paper, we describe the design, implementation, and evaluation of this computer vision system. Using this system, real-time obstacle detection was performed and digital image data were obtained successfully in flight tests conducted at NASA Langley Research Center in January and September 1999. The system is described in detail so that other researchers can easily replicate the work.

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Technology Assessment and Development of Large Deployable Antennas

A National Aeronautics and Space Administration (NASA) research and technology program called the large deployable antenna (LDA) program was initiated in early 1989 by NASA Langley Research Center to investigate and demonstrate the availability of critical technologies for passive microwave imagers. The NASA Office of Aeronautics, Exploration, and Technology (OAET) sponsored this research program to provide advanced sensor technologies for mission to planet Earth remote sensing applications. The goal of the OAET program is to provide the technology needed to enable and enhance the long‐term observations, documentation, and understanding of the Earth as a system. The LDA program involved university, industry, and NASA researchers and technologists with a range of skills and experience from electromagnetic theory to advanced materials and deployable structures. The study approach involved determining basic operational parameters and configurations for a geosynchronous wide‐scanning radiometer from which specific structural requirements were used as goals (rather than specifications) with which specific technologies could be evaluated. The study team performed a detailed technology review, evaluated the feasibility and technology readiness for a large dual‐reflector radiometer, and developed a system concept for a 25 m deployable radiometer. This paper describes the science objectives, reviews the current state of the art, presents electromagnetic configurations under consideration, and discusses the mechanical systems development effort.