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Thomas F. Lee

Abstract

This note discusses a Geostationary Operational Environmental Satellite product that can reveal the low clouds associated with tropical cyclones at night. It is based on a pixel-by-pixel difference of the longwave (10.8 μm) and shortwave (3.9 μm) brightness temperature fields. This product is compared with daytime visible images from the same satellite and passive microwave images from the Tropical Rainfall Measuring Mission Microwave Imager and the Defense Meteorological Satellite Program Special Sensor Microwave/Imager. Implications for weather analysis and forecasting are discussed for weak and shearing systems.

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Thomas F. Lee

Abstract

Visible and infrared (IR) images from the National Oceanic and Atmospheric Administration's (NOAA's) Advanced Very High Resolution Radiometer are composited to improve the depiction of airborne dust over coastlines. On IR images, wind-raised dust stands out well against heated land surfaces. Once advected over ocean, however, dust on IR images can not be easily distinguished from the cool surface. The situation is reversed on visible images: dust contrasts well with dark ocean backgrounds but poorly with bright land surfaces. To illustrate the optimal use of both data types, a composite image juxtaposes visible data over water with IR data over land. Accompanying synoptic data provide additional information about the distribution of dust in the vertical.

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Thomas F. Lee, Susan Atwater, and Charles Samuels

Abstract

The authors develop and discuss satellite image enhancements of sea ice boundaries to the north and west of Alaska. Using data from the NOAA Advanced Very High Resolution Radiometer (AVHRR), the authors illustrate how a pixel-by-pixel difference image of the two AVHRR solar channels can suppress the effects of optically thin cloud cover, revealing underlying detail. These difference images are compared to satellite ice products derived from the DMSP Special Sensor Microwave Imager (SSM/I).

AVHRR enhancements have improved daily operational support to fishing, crabbing, scientific research, and especially oil exploration in the coastal waters of Alaska. In particular, the AVHRR solar difference image has greatly facilitated the preparation of daily maps depicting the major ice edge. During a two-week period in 1991 characterized by frequent cloudiness, analysts were able to prepare information locating the major ice edge 90 percent of the time using this product. The potential of SSM/I ice products, new in nonmilitary ice edge mapping support, is also discussed.

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Gregory Thompson, Randy Bullock, and Thomas F. Lee

Abstract

Overprediction of the spatial extent of aircraft icing is a major problem in forecaster products based on numerical model output. Dependence on relative humidity fields, which are inherently broad and smooth, is the cause of this difficulty. Using multispectral satellite analysis based on NOAA Advanced Very High Resolution Radiometer data, this paper shows how the spatial extent of icing potential based on model output can be reduced where there are no subfreezing cloud tops and, therefore, where icing is unlikely. Fifty-one cases were analyzed using two scenarios: 1) model output only and 2) model output screened by a satellite cloud analysis. Average area efficiency, a statistical validation measure of icing potential using coincident pilot reports of icing, improved substantially when satellite screening was applied.

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Thomas F. Lee and James S. Boyle

Abstract

Near-surface wind speed analyses from the Special Microwave/Imager (SSM/I) are compared with those from an operational numerical forecast system. Substantial agreement exists, especially over open ocean. Nevertheless, the use of both fields together should lead to a better understanding of the synoptic situation than the use of either field alone. The SSM/I winds give a superior representation of spatial variations of wind speeds. Also, the SSM/I information can he used to examine continental influences on marine wind speeds. Such mesoscale effects are not analyzed well by global numerical models. On the other hand, the output from the numerical forecast system provides wind direction, a parameter not available from the SSM/I. In addition, forecast system winds fill in information between satellite passes and in regions contaminated by precipitation.

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Thomas F. Lee, F. Joseph Turk, and Kim Richardson

Abstract

Using data from the GOES-8–9 imager, this paper discusses the potential for consistent, around-the-clock image products that can trace the movement and evolution of low, stratiform clouds. In particular, the paper discusses how bispectral image sequences based on the shortwave (3.9 μm) and longwave (10.7 μm) infrared channels can be developed for this purpose. These sequences can be animated to produce useful loops. The techniques address several problems faced by operational forecasters in the tracking of low clouds. Low clouds are often difficult or impossible to detect at night because of the poor thermal contrast with the background on infrared images. During the day, although solar reflection makes low, stratiform clouds bright on GOES visible images, it is difficult to distinguish low clouds from adjacent ground snowcover or dense cirrus overcasts. The shortwave infrared channel often gives a superior delineation of low clouds on images because water droplets produce much higher reflectances than ice clouds or ground snowcover. Combined with the longwave channel, the shortwave channel can be used to derive products that can distinguish low clouds from the background at any time of day or night. The first case study discusses cloud properties as observed from the shortwave channels from the polar-orbiting Advanced Very High Resolution Radiometer, as well as GOES-9, and applies a correction to produce shortwave reflectance. A second case study illustrates the use of the GOES-8 shortwave channel to observe the aftermath of a spring snowstorm in the Ohio Valley. Finally, the paper discusses a red–blue–green color combination technique to build useful forecaster products.

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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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Thomas F. Lee, James R. Clark, and Steven D. Swadley

Abstract

Images of integrated cloud liquid water derived from the Special Sensor Microwave Imager (SSM/I) aboard the Defense Meteorological Satellite Program polar-orbiting satellite are presented. Examples with infrared and visible images and synoptic charts are shown for the Gulf of Alaska and Bering Sea for March 1992. The SSM/I images often show detailed, low-level cloud circulations not suggested by infrared satellite images. A prototype system for forecasting the potential for aircraft icing, which combines the SSM/I cloud liquid water parameter with numerical model output, is also presented. Where integrated cloud liquid water exceeds a specific threshold, an icing watch region is specified. The top of the icing watch layer is set to the model −20°C level or infrared cloud top, whichever is lower. The base of the icing watch layer is set to the 0°C level from model output. No watch areas are specified where the infrared cloud top temperature is above freezing, regardless of integrated cloud liquid water amount.

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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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Laurence G. Lee, Rodney F. Gonski, Eugene P. Auciello, James R. Poirier, Robert A. Marine, Steven Businger, Kenneth D. Lapenta, Robert W. Kelly, and Thomas A. NizioL

Abstract

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