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Thomas F. Lee
,
Steven D. Miller
,
Carl Schueler
, and
Shawn Miller

Abstract

The Visible/Infrared Imager Radiometer Suite (VIIRS), scheduled to fly on the satellites of the National Polar-orbiting Operational Environmental Satellite System, will combine the missions of the Advanced Very High Resolution Radiometer (AVHRR), which flies on current National Oceanic and Atmospheric Administration satellites, and the Operational Linescan System aboard the Defense Meteorological Satellite Program satellites. VIIRS will offer a number of improvements to weather forecasters. First, because of a sophisticated downlink and relay system, VIIRS latencies will be 30 min or less around the globe, improving the timeliness and therefore the operational usefulness of the images. Second, with 22 channels, VIIRS will offer many more products than its predecessors. As an example, a true-color simulation is shown using data from the Earth Observing System’s Moderate Resolution Imaging Spectroradiometer (MODIS), an application current geostationary imagers cannot produce because of a missing “green” wavelength channel. Third, VIIRS images will have improved quality. Through a unique pixel aggregation strategy, VIIRS pixels will not expand rapidly toward the edge of a scan like those of MODIS or AVHRR. Data will retain nearly the same resolution at the edge of the swath as at nadir. Graphs and image simulations depict the improvement in output image quality. Last, the NexSat Web site, which provides near-real-time simulations of VIIRS products, is introduced.

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Harald E. Krogstad
,
R. Lee Gordon
, and
Martin C. Miller

Abstract

The paper discusses the estimation of directional wave spectra by the Iterative Maximum Likelihood Method. The performance of the estimate is illustrated using data obtained by an Acoustic Doppler Current Meter in the CUrrent Measurement EXperiment (CUMEX) in the Norwegian Sea.

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Lee-Lueng Fu
,
Ichiro Fukumori
, and
Robert N. Miller

Abstract

The Geosat altimeter sea level observations in the tropical Pacific Ocean are used to evaluate the Performance of a linear wind-driven equatorial wave model. The question posed is the extent to which such a model can describe the observed sea level variations. The Kalman filter and optimal smoother are used to obtain a solution that is an optimal fit to the observation in a weighted least-squares sense. The total mean variance of the Geosat sea level observation is 98.1 cm2, of which 36.6 cm2 is due to measurement errors, leaving 61.5 cm2 for the oceanographic signal to be explained. The model is found to account for about 68% of this signal Variance and the remainder is ascribed to the effects of physical mechanisms missing from the model. This result suggests that the Geosat data contains sufficient information for testing yet more sophisticated models. Utility of an approximate filter and smoother based on the asymptotic time limit of the estimation error covariance is also examined and compared with the estimates of the full time-evolving filter. The results are found to be statistically indistinguishable from each other, but the computational requirements are more than an order of magnitude less for the approximate filter/smoother. Corrections to the wind field that drives the model are also obtained by the smoother, but they are found only to be marginally improved when compared with in situ wind measurements. The substantial errors in the Geosat data and the simplicity of the present model prevents a reliable wind estimate from being made.

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Steven D. Miller
,
Thomas F. Lee
, and
Robert L. Fennimore

Abstract

This paper presents two multispectral enhancement techniques for distinguishing between regions of cloud and snow cover using optical spectrum passive radiometer satellite observations from the Moderate Resolution Imaging Spectroradiometer (MODIS). Fundamental to the techniques are the 1.6- and 2.2-μm shortwave infrared bands that are useful in distinguishing between absorbing snow cover (having low reflectance) and less absorbing liquid-phase clouds (higher reflectance). The 1.38-μm band helps to overcome ambiguities that arise in the case of optically thin cirrus. Designed to provide straightforward, stand-alone environmental characterization for operational forecasters (e.g., military weather forecasters in the context of mission planning), these products portray the information that is contained within complex scenes as value-added, readily interpretable imagery at the highest available spatial resolution. Their utility in scene characterization and quality control of digital snow maps is demonstrated.

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Kerry Emanuel
,
Frauke Hoss
,
David Keith
,
Zhiming Kuang
,
Julie Lundquist
, and
Lee Miller
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Steven D. Miller
,
Cynthia L. Combs
,
Stanley Q. Kidder
, and
Thomas F. Lee

Abstract

The next-generation U.S. polar-orbiting environmental satellite program, the Joint Polar Satellite System (JPSS), promises unprecedented capabilities for nighttime remote sensing by way of the day/night band (DNB) low-light visible sensor. The DNB will use moonlight illumination to characterize properties of the atmosphere and surface that conventionally have been limited to daytime observations. Since the moon is a highly variable source of visible light, an important question is where and when various levels of lunar illumination will be available. Here, nighttime moonlight availability was examined based on simulations done in the context of Visible/Infrared Imager Radiometer Suite (VIIRS)/DNB coverage and sensitivity. Results indicate that roughly 45% of all JPSS-orbit [sun-synchronous, 1330 local equatorial crossing time on the ascending node (LTAN)] nighttime observations in the tropics and midlatitudes would provide levels of moonlight at crescent moon or greater. Two other orbits, 1730 and 2130 LTAN, were also considered. The inclusion of a 2130 LTAN satellite would provide similar availability to 1330 LTAN in terms of total moonlit nights, but with approximately a third of those nights being additional because of this orbit’s capture of a different portion of the lunar cycle. Nighttime availability is highly variable for near-terminator orbits. A 1-h shift from the 1730 LTAN near-terminator orbit to 1630 LTAN would nearly double the nighttime availability globally from this orbit, including expanded availability at midlatitudes. In contrast, a later shift to 1830 LTAN has a negligible effect. The results are intended to provide high-level guidance for mission planners, algorithm developers, and various users of low-light applications from these future satellite programs.

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Richard L. Bankert
,
Jeremy E. Solbrig
,
Thomas F. Lee
, and
Steven D. Miller

Abstract

The Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) nighttime visible channel was designed to detect earth–atmosphere features under conditions of low illumination (e.g., near the solar terminator or via moonlight reflection). However, this sensor also detects visible light emissions from various terrestrial sources (both natural and anthropogenic), including lightning-illuminated thunderstorm tops. This research presents an automated technique for objectively identifying and enhancing the bright steaks associated with lightning flashes, even in the presence of lunar illumination, derived from OLS imagery. A line-directional filter is applied to the data in order to identify lightning strike features and an associated false color imagery product enhances this information while minimizing false alarms. Comparisons of this satellite product to U.S. National Lightning Detection Network (NLDN) data in one case as well as to a lightning mapping array (LMA) in another case demonstrate general consistency to within the expected limits of detection. This algorithm is potentially useful in either finding or confirming electrically active storms anywhere on the globe, particularly those occurring in remote areas where surface-based observations are not available. Additionally, the OLS nighttime visible sensor provides heritage data for examining the potential usefulness of the Visible-Infrared Imager-Radiometer Suite (VIIRS) Day/Night Band (DNB) on future satellites including the National Polar-orbiting Operational Environmental Satellite System (NPOESS) Preparatory Project (NPP). The VIIRS DNB will offer several improvements to the legacy OLS nighttime visible channel, including full calibration and collocation with 21 narrowband spectral channels.

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Jared A. Lee
,
Sue Ellen Haupt
,
Pedro A. Jiménez
,
Matthew A. Rogers
,
Steven D. Miller
, and
Tyler C. McCandless

Abstract

The Sun4Cast solar power forecasting system, designed to predict solar irradiance and power generation at solar farms, is composed of several component models operating on both the nowcasting (0–6 h) and day-ahead forecast horizons. The different nowcasting models include a statistical forecasting model (StatCast), two satellite-based forecasting models [the Cooperative Institute for Research in the Atmosphere Nowcast (CIRACast) and the Multisensor Advection-Diffusion Nowcast (MADCast)], and a numerical weather prediction model (WRF-Solar). It is important to better understand and assess the strengths and weaknesses of these short-range models to facilitate further improvements. To that end, each of these models, including four WRF-Solar configurations, was evaluated for four case days in April 2014. For each model, the 15-min average predicted global horizontal irradiance (GHI) was compared with GHI observations from a network of seven pyranometers operated by the Sacramento Municipal Utility District (SMUD) in California. Each case day represents a canonical sky-cover regime for the SMUD region and thus represents different modeling challenges. The analysis found that each of the nowcasting models perform better or worse for particular lead times and weather situations. StatCast performs best in clear skies and for 0–1-h forecasts; CIRACast and MADCast perform reasonably well when cloud fields are not rapidly growing or dissipating; and WRF-Solar, when configured with a high-spatial-resolution aerosol climatology and a shallow cumulus parameterization, generally performs well in all situations. Further research is needed to develop an optimal dynamic blending technique that provides a single best forecast to energy utility operators.

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Thomas E. Lee
,
Steven D. Miller
,
F. Joseph Turk
,
Carl Schueler
,
Richard Julian
,
Steve Deyo
,
Patrick Dills
, and
Sherwood Wang

The National Polar-orbiting Operational Environmental Satellite System (NPOESS) will feature the Visible-Infrared Imager-Radiometer Suite (VIIRS), a 22-channel imager that will contribute to nearly half of the NPOESS environmental data records. Included on VIIRS will be the Day/Night band (DNB), a visible channel designed to image the Earth and its atmosphere in all conditions ranging from bright solar illumination, to nocturnal lunar illumination, and negligible external illumination. Drawing heritage from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) instruments orbiting since the late 1960s, the DNB will be used to detect clouds at night, understand patterns of urban development based on the emissions of cities, monitor fires, and image scenes of snow and ice at the surface of the Earth. Thanks to significant engineering improvements, the DNB will produce superior capabilities to the OLS for a number of new applications.

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Steven D. Miller
,
Jeffrey D. Hawkins
,
John Kent
,
F. Joseph Turk
,
Thomas F. Lee
,
Arunas P. Kuciauskas
,
Kim Richardson
,
Robert Wade
, and
Carl Hoffman

Under the auspices of the National Polar-orbiting Operational Environmental Satellite System's (NPOESS) Integrated Program Office (IPO), the Naval Research Laboratory (NRL) has developed “NexSat” (www.nrlmry.navy.mil/nexsat_pages/nexsat_home.html)—a public-access online demonstration over the continental United States (CONUS) of near-real-time environmental products highlighting future applications from the Visible/Infrared Imager/Radiometer Suite (VIIRS). Based on a collection of operational and research-grade satellite observing systems, NexSat products include the detection, enhancement, and where applicable, physical retrieval of deep convection, low clouds, light sources at night, rainfall, snow cover, aircraft contrails, thin cirrus layers, dust storms, and cloud/aerosol properties, all presented in the context of value-added imagery. The purpose of NexSat is threefold: 1) to communicate the advanced capabilities anticipated from VIIRS, 2) to present this information in near–real time for use by forecasters, resource managers, emergency response teams, civic planners, the aviation community, and various government agencies, and 3) to augment the NRL algorithm development multisensor/model-fusion test bed for accelerated transitions to operations during the NPOESS era. This paper presents an overview of NexSat, highlighting selected products from the diverse meteorological phenomenology over the CONUS.

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