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Bhatt R.,Science Systems And Applications Inc. | Doelling D.R.,Science Systems And Applications Inc. | Morstad D.,National Aeronautics and Space Administration Langley Research Center | Scarino B.R.,Science Systems And Applications Inc. | Gopalan A.,Science Systems And Applications Inc.
IEEE Transactions on Geoscience and Remote Sensing | Year: 2014

A desert daily exoatmospheric radiance model (DERM) based on a well-calibrated (reference) geostationary Earth orbit (GEO) satellite visible sensor can be used to transfer the calibration to a (target) GEO sensor located at the same equatorial longitude location. The DERM is based on the reference GEO daily radiances observed over a single pseudoinvariant calibration site (PICS) being that the daily angular conditions are repeated annually for any historical or successive colocated GEO. The GEO-specific PICSs used in the study are first inspected using the well-calibrated Aqua-MODerate Resolution Imaging Spectroradiometer (MODIS) exoatmospheric reflectances for stability. The Libyan Desert site was found to be stable within 1$% over ten years. The average clear-sky daily local-noon interannual variability based on Meteosat-9 0.65- μm top-of-atmosphere radiances over the Libyan Desert is 0.74$%, which implies that the combined surface and atmospheric column is invariant. A spectral band adjustment factor, based on Scanning Imaging Absorption Spectrometer for Atmospheric Cartography spectral radiances, is used to account for sensor spectral response function (SRF) differences between the reference and target GEO. The GEO reference calibration was based on the GEO/Aqua-MODIS ray-matched radiance intercalibration transfer technique. The reference Meteosat-9 DERM and ray-matched calibration consistency was within 0.4% and 1.9 % for Meteosat-8 and Meteosat-7, respectively. Similarly, GOES-10 and GOES-15 were calibrated based on the GOES-11 DERM using the Sonoran Desert and were found to have a consistency within 1% and 3 %, respectively. © 2013 IEEE. Source


Lopez D.H.,University of Arizona | Rabbani M.R.,University of Arizona | Crosbie E.,National Aeronautics and Space Administration Langley Research Center | Crosbie E.,Oak Ridge Associated Universities | And 3 more authors.
Atmosphere | Year: 2016

This study uses more than a decade's worth of data across Arizona to characterize the spatiotemporal distribution, frequency, and source of extreme aerosol events, defined as when the concentration of a species on a particular day exceeds that of the average plus two standard deviations for that given month. Depending on which of eight sites studied, between 5% and 7% of the total days exhibited an extreme aerosol event due to either extreme levels of PM10, PM2.5, and/or fine soil. Grand Canyon exhibited the most extreme event days (120, i.e., 7% of its total days). Fine soil is the pollutant type that most frequently impacted multiple sites at once at an extreme level. PM10, PM2.5, fine soil, non-Asian dust, and Elemental Carbon extreme events occurred most frequently in August. Nearly all Asian dust extreme events occurred between March and June. Extreme Elemental Carbon events have decreased as a function of time with statistical significance, while other pollutant categories did not show any significant change. Extreme events were most frequent for the various pollutant categories on either Wednesday or Thursday, but there was no statistically significant difference in the number of events on any particular day or on weekends versus weekdays. © 2015 by the authors. Source


Hibbard K.,Johns Hopkins University | Glaze L.,NASA | Prince J.,National Aeronautics and Space Administration Langley Research Center
61st International Astronautical Congress 2010, IAC 2010 | Year: 2010

Venus remains one of the great-unexplored planets in our solar system with key questions remaining on the evolution of its atmosphere and climate, volatile cycles, and the thermal and magmatic evolution of the planet's surface. One potential approach toward answering these questions is to fly a reconnaissance mission that utilizes a multi-mode radar in a near-circular low-altitude orbit of approximately 400 km and 60-70° inclination. This type of mission profile results in a total mission delta-V of approximately 4.4 km/s. Aerobraking could provide for a significant portion, potentially up to half, of this energy transfer, thereby permitting more mass to be allocated to the spacecraft and science payload or facilitating the use of smaller, cheaper launch vehicles. Aerobraking at Venus also provides additional science benefits through measurements of upper atmospheric density (recovered from accelerometer data) and temperature values, especially near the terminator where temperature changes are abrupt and constant pressure levels drop dramatically in altitude from day to night. The scientifically rich Venus is also an ideal location to utilize aerobraking techniques. Venus's thick lower atmosphere and slow planet rotation results in more predictable atmospheric densities. The Venus atmosphere has a density variation of 8% compared to Mars' 30% variability. In general, most aerobraking missions try to minimize the duration of the aerobraking phase to keep costs down. These short phases have limited margin to account for contingencies. It is the stable and predictive nature of Venus's atmosphere that provides safer aerobraking opportunities. The nature of aerobraking at Venus provides ideal opportunities to demonstrate aerobraking enhancements and techniques yet to be used at Mars, such as flying a temperature corridor (vs. a heat rate corridor) using a thermal response surface algorithms and autonomous aerobraking, shifting many daily ground activities to onboard the spacecraft. Defining an aerobraking temperature corridor, based on spacecraft component maximum temperatures, can be employed on a spacecraft specifically designed for aerobraking, and will predict subsequent aerobraking orbits and prescribe apoapsis propulsive maneuvers to maintain the spacecraft with its specified temperature limits. A spacecraft specifically designed for aerobraking in the Venus environment can provide a cost-effective platform for achieving these expanded science and technology goals. This paper will discuss the science merits of a low-altitude circular orbit at Venus, highlight the differences in aerobraking at Venus versus Mars, and presents design data using a flight system specifically designed for an aerobraking mission at Venus to achieve new science and technology heights. Copyright © 2010 by the International Astronautical Federation. All rights reserved. Source


Van Weverberg K.,Brookhaven National Laboratory | Van Weverberg K.,Catholic University of Louvain | Vogelmann A.M.,Brookhaven National Laboratory | Lin W.,Brookhaven National Laboratory | And 6 more authors.
Journal of the Atmospheric Sciences | Year: 2013

This paper presents a detailed analysis of convection-permitting cloud simulations, aimed at increasing the understanding of the role of parameterized cloud microphysics in the simulation of mesoscale convective systems (MCSs) in the tropical western Pacific (TWP). Simulations with three commonly used bulk microphysics parameterizations with varying complexity have been compared against satellite-retrieved cloud properties. An MCS identification and tracking algorithm was applied to the observations and the simulations to evaluate the number, spatial extent, and microphysical properties of individual cloud systems. Different from many previous studies, these individual cloud systems could be tracked over larger distances because of the large TWP domain studied. The analysis demonstrates that the simulation of MCSs is very sensitive to the parameterization of microphysical processes. The most crucial element was found to be the fall velocity of frozen condensate. Differences in this fall velocity between the experiments were more related to differences in particle number concentrations than to fall speed parameterization. Microphysics schemes that exhibit slow sedimentation rates for ice aloft experience a larger buildup of condensate in the upper troposphere. This leads to more numerous and/or larger MCSs with larger anvils. Mean surface precipitation was found to be overestimated and insensitive to the microphysical schemes employed in this study. In terms of the investigated properties, the performances of complex two-moment schemes were not superior to the simpler one-moment schemes, since explicit prediction of number concentration does not necessarily improve processes such as ice nucleation, the aggregation of ice crystals into snowflakes, and their sedimentation characteristics. © 2013 American Meteorological Society. Source


Khlopenkov K.V.,Science Systems And Applications Inc. | Doelling D.R.,National Aeronautics and Space Administration Langley Research Center | Okuyama A.,Japan Meteorological Agency
IEEE Transactions on Geoscience and Remote Sensing | Year: 2015

An image processing methodology is presented to recover the quality of the Multifunctional Transport Satellite (MTSAT)-1R visible channel data affected by spatial crosstalk. The slight blurring of the visible optical path is attributed to an imperfection in the mirror surface caused either by flawed polishing or a dust contaminant. The methodology assumes that the dispersed portion of the signal is small and distributed randomly around the optical axis, which allows the image to be deconvolved using an inverted point spread function (PSF). The PSF is described by four parameters, which are solved using a maximum-likelihood estimator using coincident collocated MTSAT-2 images as truth. A subpixel image matching technique is used to align the MTSAT-2 pixels into the MTSAT-1R projection and to correct for navigation errors and cloud displacement due to the time and viewing geometry differences between the two satellite observations. An optimal set of the PSF parameters is derived by an iterative routine based on the 4-D Powell's conjugate direction method that minimizes the difference between the PSF-corrected MTSAT-1R and the collocated MTSAT-2 images. The PSF parameters were found to be consistent over the 5 days of available daytime coincident and MTSAT-1R and MTSAT-2 images. After applying the PSF parameters, the visible sensor response is nearly linear, and the space count is close to zero. The overall linear regression standard error was reduced by 52%. Users can easily apply the PSF parameter coefficients to the MTSAT-1R imager pixel level counts to restore the original quality of the entire MTSAT-1R record. © 1980-2012 IEEE. Source

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