Time filter

Source Type

Rockville, MD, United States

Sun B.,Im Systems Group | Sun B.,The Center for Satellite Applications and Research | Reale A.,The Center for Satellite Applications and Research | Seidel D.J.,National Oceanic and Atmospheric Administration | Hunt D.C.,University Corporation for Atmospheric Research
Journal of Geophysical Research: Atmospheres

Collocated global atmospheric temperature, humidity, and refractivity profiles from radiosondes and from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation data for April 2008 to October 2009 are compared for two purposes. The first is to quantify the error characteristics of 12 radiosonde types flown in the global operational network, as a function of height and for both day and nighttime observations, for each of the three variables. The second is to determine the effects of imperfect temporal and spatial collocation on the radiosonde-COSMIC differences, for application to the general problem of satellite calibration and validation using in situ sounding data. Statistical analyses of the comparisons reveal differences among radiosonde types in refractivity, relative humidity, and radiation-corrected temperature data. Most of the radiosonde types show a dry bias, particularly in the upper troposphere, with the bias in daytime drier than in nighttime. Weather-scale variability, introduced by collocation time and distance mismatch, affects the comparison of radiosonde and COSMIC data by increasing the standard deviation errors, which are generally proportional to the size of the time and distance mismatch within the collocation window of 6 h and 250 km considered. Globally, in the troposphere (850-200 hPa), the collocation mismatch impacts on the comparison standard deviation errors for temperature are 0.35 K per 3 h and 0.42 K per 100 km and, for relative humidity, are 3.3% per 3 h and 3.1% per 100 km, indicating an approximate equivalence of 3 h to 100 km in terms of mismatch impact. Copyright 2010 by the American Geophysical Union. Source

Bangert M.,Karlsruhe Institute of Technology | Nenes A.,Georgia Institute of Technology | Vogel B.,Karlsruhe Institute of Technology | Vogel H.,Karlsruhe Institute of Technology | And 7 more authors.
Atmospheric Chemistry and Physics

We investigated the impact of mineral dust particles on clouds, radiation and atmospheric state during a strong Saharan dust event over Europe in May 2008, applying a comprehensive online-coupled regional model framework that explicitly treats particle microphysics and chemical composition. Sophisticated parameterizations for aerosol activation and ice nucleation, together with two-moment cloud microphysics are used to calculate the interaction of the different particles with clouds depending on their physical and chemical properties. The impact of dust on cloud droplet number concentration was found to be low, with just a slight increase in cloud droplet number concentration for both uncoated and coated dust. For temperatures lower than the level of homogeneous freezing, no significant impact of dust on the number and mass concentration of ice crystals was found, though the concentration of frozen dust particles reached up to 100 l -1 during the ice nucleation events. Mineral dust particles were found to have the largest impact on clouds in a temperature range between freezing level and the level of homogeneous freezing, where they determined the number concentration of ice crystals due to efficient heterogeneous freezing of the dust particles and modified the glaciation of mixed phase clouds. Our simulations show that during the dust events, ice crystals concentrations were increased twofold in this temperature range (compared to if dust interactions are neglected). This had a significant impact on the cloud optical properties, causing a reduction in the incoming short-wave radiation at the surface up to-75 W m -2. Including the direct interaction of dust with radiation caused an additional reduction in the incoming short-wave radiation by 40 to 80 W m -2, and the incoming long-wave radiation at the surface was increased significantly in the order of +10 W m -2. The strong radiative forcings associated with dust caused a reduction in surface temperature in the order of-0.2 to-0.5 K for most parts of France, Germany, and Italy during the dust event. The maximum difference in surface temperature was found in the East of France, the Benelux, and Western Germany with up to-1 K. This magnitude of temperature change was sufficient to explain a systematic bias in numerical weather forecasts during the period of the dust event. © 2012 Author(s). Source

Levine A.S.,San Diego State University | Levine A.S.,Im Systems Group | Feinholz C.L.,Pacific Cartography
Applied Geography

Sociospatial information is critical to marine and coastal ecosystem management. The Hawaii Coastal Uses Mapping Project used a participatory geographic information systems (PGIS) methodology to gather local knowledge regarding the location and intensity of coastal human activities in Hawaii's priority sites for coral reef management. PGIS provided an efficient and effective means of obtaining information in a data-poor context, particularly at a scale and location where considerable local knowledge is held by community members and resource users. We detail the PGIS methods developed to collect sociospatial data on human uses in the project regions and discuss important considerations regarding the practice of PGIS that emerged from the mapping process, as well as implications for the production and documentation of spatial knowledge. Key themes include: issues of scale and appropriateness in using PGIS as a method for mapping human coastal and marine activities; data validity, authority, and the nature of local knowledge; community trust, engagement, and collaboration; and utility for coral reef management. While several factors limit local agencies' ability to use this spatial information to date, natural resource managers found the participatory mapping process to be highly valuable for stakeholder identification and engagement, and the maps provide a resource to state and federal managers to better understand the human implications of future management scenarios. © 2014 The Authors. Source

Vargas M.,National Oceanic and Atmospheric Administration | Miura T.,University of Hawaii at Manoa | Shabanov N.,Im Systems Group | Kato A.,University of Hawaii at Manoa
Journal of Geophysical Research: Atmospheres

The Suomi National Polar-orbiting Partnership (S-NPP) satellite with Visible/Infrared Imager/Radiometer Suite (VIIRS) onboard was launched in October 2011. VIIRS is the primary instrument for a suite of Environmental Data Records (EDR), including Vegetation Index (VI) EDR, for weather forecasting and climate research. The VIIRS VI EDR operational product consists of the Top of the Atmosphere (TOA) Normalized Difference Vegetation Index (NDVI), the Top of the Canopy (TOC) Enhanced Vegetation Index (EVI), and per-pixel product quality information. In this paper, we report results of our assessment of the early VIIRS VI EDR (beta quality) using Aqua MODIS and NOAA-18 AVHRR/3 as a reference for May 2012 to March 2013. We conducted two types of analyses focused on an assessment of physical (global scale) and radiometric (regional scale) performances of VIIRS VI EDR. Both TOA NDVI and TOC EVI of VIIRS showed spatial and temporal trends consistent with the MODIS counterparts, whereas VIIRS TOA NDVI was systematically higher than that of AVHRR. Performance of the early VIIRS VI EDR was limited by a lack of adequate per-pixel quality information, commission/omission errors of the cloud mask, and uncertainties associated with the surface reflectance retrievals. A number of enhancements to the VI EDR are planned, including: (1) implementation of a TOC EVI back-up algorithm, (2) addition of more detailed quality flags on aerosols, clouds, and snow cover, and (3) implementation of gridding and temporal compositing. A web-based, product quality monitoring tool has been developed and automated product validation protocols are being prototyped. Key Points Present initial results of assessment of the VIIRS VI EDR product after launch VI showed good product integrity and was found radiometrically performing well VI is beta quality and users are warned that the product still contains errors ©2013. American Geophysical Union. All Rights Reserved. Source

Shi W.,The Center for Satellite Applications and Research | Shi W.,Colorado State University | Wang M.,The Center for Satellite Applications and Research | Li X.,The Center for Satellite Applications and Research | And 2 more authors.
Remote Sensing of Environment

Satellite measurements from Synthetic Aperture Radar (SAR) and the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua platform are used to study the ocean sand ridges in the eastern Bohai Sea in China. Even though the imaging mechanisms for SAR and MODIS-Aqua remote sensing are different, the sand ridges are shown to have exactly the same patterns in images from both sensors. Therefore, the location, extension and coverage of the ocean sand ridges can be detected and cross-examined by both SAR and MODIS-Aqua observations. Satellite images show quite different sand ridge distribution pattern from the published bathymetry map (based on in situ data) that shows six sand ridges in the area. 10 finger-shaped sand ridges are identified from satellite observations. The tidal-current/sand-ridge interaction driven physical and optical changes are assessed and evaluated. The existence of sand ridges causes enhanced water diffuse attenuation coefficient Kd(490) and elevated normalized water-leaving radiance at the red and near-infrared (NIR) wavelengths. The sea surface over the sand ridges experiences significant seasonal variability of water turbidity and shows remarkable differences from nearby ocean regions. During winter, Kd(490) values are about 2-3m-1 over the ridges, while the maximum Kd(490) in the neighboring oceans is approximately 1.5m-1. In summer, the enhancement of the sea surface turbidity is less significant than that which occurs in winter. © 2011. Source

Discover hidden collaborations