Since the 1960s, National Aeronautics and Space Administration (NASA), has been developing Polar orbiting Operational Environmental Satellites (POES) for National Oceanic and Atmospheric Administration (NOAA). NOAA-M, renamed as NOAA-17, the third in the KLM series of POES satellites, was launched successfully on June 24, 2002 from Vandenberg Air Force Base, California. The satellite has been placed in a sun-synchronous orbit at an altitude of 833 Km with an inclination angle of 98.60 with respect to the Equator. The orbital period is 101.35 minutes and equatorial crossing time is 10 A.M. The spacecraft like its predecessors carries a suite of sensors on-board. NRSC has been providing NOAA data to the Indian user community since 1987. From 01 April, 2004 onwards, NRSC is acquiring data from NOAA-17 satellite also. Currently, out of the available suite of sensors, NRSC acquires only Advanced Very High Resolution Radiometer (AVHRR ) data. NOAA-17 AVHRR is similar to NOAA-16 AVHRR except that it includes a new sixth channel in the visible range that can be used to provide the capability to distinguish between clouds and snow/ice on the ground. The AVHRR sensor provides data with a spatial resolution of 1.09 Km and 10 bit radiometric quantization. All six spectral channels of the sensor are registered so that they all measure energy from the same spot on the earth at the same time.
Although the AVHRR has six channels, only five are transmitted to the ground at any one time. Channels 3A and 3B cannot be operated simultaneously. Channel 3A is useful for snow - cloud discrimination, while Channel 3B is useful for Sea Surface Temperature (SST) measurements. In view of the above, during day passes Channel 3A data is acquired, while during night passes Channel 3B data is acquired by default. NOAA digital data is supplied to users in a predefined format called Level-1B format defined by NOAA. Other organizations in the world, who supply the data, follow the same format. It is a packed format and all the band data exists in a 10 bit format. The data product, in addition to video data, contains ancillary information like Earth Location Points (ELPs), solar zenith angle and calibration. All the commercially available Image Analysis Packages have the facility to read data in Level-1B format.The current Level-1B format has been modified from NOAA - 15 data onwards. Currently NRSC is acquiring data from NOAA-17 and NOAA-18. Differences between old and new NOAA /AVHRR Level-1B formats. More mission details at
NOAA Web site .