.

Satellite meteorology

作者:
R.R. Kelkar
ISBN :
9788178001371
出版日期:
2011-03-19 00:00:00
语言:
国家地区:
.
144Satellite Meteorologyparameter and transmit the data to a ground station. In a radiosonde, which is the most widely used instrument for this purpose, an electronic package with a transmitter is attached to the balloon and the sensors measure pressure, temperature and humidity at various levels as the balloon rises. The signals received at a ground station are decoded to obtain the vertical profiles of temperature, humidity and other parameters. Most upper air stations take two radiosonde ascents per day at the synoptic hours of 00 and 12 UTe. Radiosonde data also have their own inherent errors due to solar radiation during daytime and infrared cooling at night. The time lag between the temperature and humidity measurements and errors in pressure measurement add further to the overall errors and uncertainties (McMillin et al 1988). In addition, national meteorological services use radiosonde instruments of different makes and designs, and employ different ground computation procedures. This requires them to undertake rigorous inter-comparisons periodically so as to maintain compatibility amongst the instruments and uniformity in the global synoptic analyses. In an attempt to make use of data from INSAT satellites which did not have a sounder, Prasad et al (1998) developed a technique to estimate tropospheric moisture profiles from INSA T IR digital data to generate moisture fields at various levels for purposes of initialization of numerical models. Such information can be used a proxy for direct satellite soundings. Polar orbiting satellites and some geostationary satellites can now provide a repetitive, globally consistent sounding capability on land and oceanic areas alike. The soundings are available on a finer grid but they differ from the radiosonde in the scale on which they sample the atmosphere in both horizontal and vertical dimensions. While the radiosonde measures the local environment, satellite profiles are averages of horizontal and relatively deeper layers of the atmosphere. Absolute accuracy of satellite soundings is difficult to establish. With every satellite pass, a fresh retrieval is possible, hence more frequent profiles can be obtained compared to radiosondes. However, elaborate systems are required to receive the satellite data and complex software is needed to process it. Khanna et al (1993) have described the early attempts at retrieving the temperature soundings of the atmosphere over the Indian region by processing NOAA satellite data received at New Delhi with the International TOVS Processing Package. They have also explained the basic principles of the method adopted for the retrieval, which are summarized below. The narrow band radiance measurements made by a satellite depend upon the surface skin temperature and the vertical profiles of temperature and
本书内搜索
序号 页码 相关内容
您还未搜索