摘要:

This project was started in October 1985 with the objectives of (1) producing a 1 km-resolution database of Antarctica and (2) producing a 1:5 000000 scale image map. So far, 28 three-band AVHRR scenes have been corrected for variable Sun reflectance and transformed to a polar stereographic projection using a digitized coastline for control. Relatively cloud-free segments from 18 scenes have been incorporated in a provisional mosaic and further segments are to be included to improve the picture.

ISSN:0143-1161    

DOI:10.1080/01431168908903908

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Using photographic terminology for channel 3 pictures in sunshine, one notes that most ice clouds appear black and that cloud shadows are equally dark, but water droplet clouds appear in all shades. These shades also vary greatly with the direction of sunshine relative to the line of sight because scatter is almost entirely by diffraction. Droplets and ice crystals larger than about 10 fan absorb the incident radiation almost completely and it does not penetrate through clouds unless there exist plenty of unobstructed ray paths through the clouds. The reflection from a water surface is almost metallic in intensity so that glint completely saturates the radiometer. There is no evidence of comparable reflection from ice. All snow-covered surfaces, including sea ice, appear black. Stratus cloud shows large variations in reflectance depending on the state of the convection in it which brings very small droplets to the surface. Small particle size causes some contrails and orographic cirrus to appear white although most appear black; old cumulonimbus tops develop pale areas when gravitational settling leaves predominantly very small crystals at the top while still active areas remain black.

ISSN:0143-1161    

DOI:10.1080/01431168908903909

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Within the PROgramme for a Meteorological Information System (PROMIS) project in Sweden a method of multi-spectral analysis and classification of Advanced Very High Resolution Radiometer (AVHRR) data is developed. The model will be based on a statistical database of object classes and ruled by information about prevailing Sun elevations and air mass temperatures. A new system provides the image processing and data handling capacity necessary for an operational classification of AVHRR data. Operational tests will start during the beginning of 1988.

ISSN:0143-1161    

DOI:10.1080/01431168908903910

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A new method is described for obtaining information on the high latitude upper level wind field through the production of cloud motion vectors from sequences of images from polar orbiting satellites. The vectors are produced using sets of three calibrated, 11 μm AVHRR images of the polar regions from successive orbits of the TIROS-N series satellites. Two schemes have been developed for the generation of vectors based on manual and automatic techniques coupled with manual quality control. Case studies have shown that, provided the images are accurately registered and the cloud tracers are carefully selected, useful vectors may be derived.

ISSN:0143-1161    

DOI:10.1080/01431168908903911

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The infrared sensor systems AVHRR (Advanced Very High Resolution Radiometer) and HIRS (High resolution Infrared Radiation Sounder) on board the NOAA-7 satellite are studied theoretically by means of radiative transfer calculations to enable the development of new retrieval techniques for atmospheric water vapour profiles. Simulations of radiometer signals have been performed for a large set of atmospheres from the middle and tropical latitudes. Subsequent development of a physical-statistical retrieval method demonstrates the usefulness of a coupling of both radiometers for water vapour retrievals in a single HIRS field of view. Total column amounts as well as the amounts in thick layers (150-200 hPa (thick) in the lower troposphere can be derived with an accuracy of 5-15 per cent and 15-25 per cent respectively. The amounts in thinner layers (50hPa) can be estimated with accuracies between 20 and 30 per cent. The AVHRR split window channels are a powerful tool in the water vapour retrievals. The technique developed benefits from the simultaneous retrieval of temperature profiles and surface temperatures. Accounting for scan-angle dependencies explicitly leads to improved retrievals. The synergy of AVHRR with HIRS increases the number of retrievals in partially cloudy fields of view compared with HIRS retrievals alone. A case study demonstrates the capability of the method to resolve water vapour structures with a high spatial resolution and its value in areas where conventional measurements from radiosonde ascents are sparse.

ISSN:0143-1161    

DOI:10.1080/01431168908903912

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Cloud liquid water path (LWP) is an important parameter to validate forecasts obtained from circulation models of high spatial resolution. At present, it is not measured on a routine basis. Being part of the Advanced Very High Resolution Radiometer (AVHRR) Processing scheme Over cLoud, Land and Ocean (APOLLO) a parametrization scheme to derive optical thickness from cloud reflectance and, further, the LWP has been adopted and adjusted to AVHRR channel-1 counts. From these counts, top-of-atmosphere bidirectional reflectance data are obtained. Using APOLLO-derived fully cloudy pixels only, the directional hemispherical cloud reflectance is derived to which the parametrization scheme refers. The LWP of each fully cloudy pixel is determined. As a first application, the mean LWP of 63-5 × 63-5 km2boxes is computed and compared to a 14-hour forecast of the LWP made with the Europa-Modell of the Deutsche Wetterdienst. The location of the clouds seems to be forecasted rather well by the model. However, the LWP computed by the model is higher (by a factor of 4 or 5) than that derived from AVHRR data using APOLLO. A first validation by means of aircraft measurements shows that the APOLLO-derived LWP is too low by about 50 per cent. This reduces the discrepancy to the computed data but the model predicted LWP still seems to be too high by a factor of 3.

ISSN:0143-1161    

DOI:10.1080/01431168908903913

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

NOAA AVHRR (Advanced Very High Resolution Radiometer) data make a significant contribution to information about boundary layer air flow patterns, especially over complex terrain, where wind fields are very often totally disconnected from upper air flows. An evaluation procedure which is based on different approaches, depending on the regional meteorological situation, is presented in this paper. It-includes (1) mapping of local cold air pools, (2) mapping of the vertical extent of temperature inversions and (3) mapping the extent and dynamics of fog layers. All the examples refer to the Swiss Alps and the surrounding basins.

ISSN:0143-1161    

DOI:10.1080/01431168908903914

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The basic features of single- and dual-channel aerosol retrieval algorithms based on matching radiances measured in AVHRR channels -1 (∼0.58-0.68 μm) and -2( ∼0.73-1.10μm) with model computations will be described. The use of the NOAA/NESDIS single-channel algorithm will be illustrated with examples of detection and mapping of enhanced atmospheric turbidity over the oceans. The effects of variations in the physical and radiative properties of atmospheric aerosols, and in atmospheric ozone and water vapour, will be briefly discussed in the light of model sensitivity analyses.

ISSN:0143-1161    

DOI:10.1080/01431168908903915

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Volcanic aerosols are always present in the atmosphere, but because of the nature of volcanic activity their abundance varies greatly with time. The problem of detecting and monitoring volcanic ash clouds using radiance measurements from the AVHRR/2 (Advanced Very High Resolution Radiometer) instrument is discussed and some results are presented for the Galunggung eruptions of July 1982. It is shown that during the first few hours of an explosive eruption AVHRR/2 thermal channel measurements can be used to detect and discriminate volcanic clouds. Once the eruption cloud has spread and thinned out however, the problem of detection is difficult because of the similarity between dispersed volcanic cloud and semi-transparent cirrus. In these cases, if the volcanic cloud consists of liquid H2SO4droplets, then it is possible to discriminate them from water/ice clouds because of the reverse absorption effect in channel-4 and channel-5. Some evidence is presented showing this effect. It is proposed that the temperature difference image be used operationally to warn of the presence of volcanic clouds.

ISSN:0143-1161    

DOI:10.1080/01431168908903916

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Multichannel sea surface tempratures (MCSSTs) have been produced operationally on a global basis from AVHRR data since November 1981. Although the basic technique has been unchanged for over S years, refinements and modifications to handle special situations (e.g. volcanic and sandstorm aerosols) are under development and a cross-product (nonlinear) procedure for atmospheric corrections has been tested. The aerosol optical depth estimates have been made experimentally for about a year using AVHRR data from channel-1, and special cloud screening techniques have been developed to differentiate between clouds and aerosols.

ISSN:0143-1161    

DOI:10.1080/01431168908903917

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor