NAME Satellite: NOAA POES AMSU Data (level 1b) 1.0 General Information The NOAA POES ATOVS AMSU Data is one of several satellite data sets collected by the National Center for Atmospheric Reserach/Earth Observation Laboratory (NCAR/EOL) as part of the North American Monsoon Experiment (NAME) project. Included in the data set are Advanced TIROS Operational Vertical Sounder (ATOVS) Advanced Microwave Sounding Unit-A (AMSU-A) and Advanced Microwave Sounding Unit-B (AMSU-B) aboard the National Oceanic and Atmospheric Administration (NOAA) Polar Orbiting Environmental Satellites (POES). The data cover the period from 1 June to 30 September 2004 and include data from the NOAA-15, NOAA-16 and NOAA-17 satellites. Data are available at POES satellite overpass times. These data were acquired from the NOAA Comprehensive Large Array-data Stewardship System (CLASS; www.class.noaa.gov) and are in level1B format. Any passes that had any portion over the NAME Tier 1 region (20-35N and 105-115W) are included within this data set. 2.0 Data Contact NOAA CLASS contact: NOAA CLASS Help Desk info@class.noaa.gov NCAR/EOL contact: Scot Loehrer (loehrer@ucar.edu) 3.0 Data and Format Information TOVS/ATOVS Introduction The TIROS Operational Vertical Sounder (TOVS) system consists of three separate instruments: the High Resolution Infrared Radiation Sounder Version 2 (HIRS/2), the Microwave Sounding Unit (MSU) and the Stratospheric Sounding Unit (SSU). Each instrument has different characteristics, resolutions, scan properties, etc. which are described below. This system is onboard the NOAA 6 through NOAA 14 and TIROS-N satellites. TOVS was designed so that the data from the HIRS/2, SSU and MSU instruments could be combined to compute: 1) atmospheric temperature profiles from the surface to 10 millibars (mb), 2) water vapor content at three levels of the atmosphere, and 3) total ozone content. Improved accuracy of retrieval profiles and a better definition of the water vapor profile, even in the presence of clouds, are the objectives of this system. In the Advanced TOVS (ATOVS) system, the Advanced Microwave Sounding Unit-A (AMSU-A) and the Advanced Microwave Sounding Unit-B (AMSU-B) replace the MSU and the SSU, while the High Resolution Infrared Radiation Sounder Version 3 (HIRS/3) replaces the HIRS/2. All three ATOVS instruments, AMSU-A, AMSU-B, and HIRS/3, are onboard the NOAA KLM series of satellites which fields NOAA 15, NOAA 16 and NOAA 17. Each instrument has different characteristics, resolutions, scan properties, etc. which are described below. AMSU-A Introduction The Advanced Microwave Sounding Unit-A (AMSU-A) is part of the ATOVS instrument suite flown onboard the NOAA KLM series of satellites. The AMSU-A is a multi-channel microwave radiometer used for measuring global atmospheric temperature profiles and for gathering information on atmospheric water in all of its forms, save small ice particles which are transparent at microwave frequencies. AMSU-A is a cross-track, line-scanned instrument designed to measure scene radiances in 15 discrete frequency channels. These measurements permit the calculation of the vertical temperature profile from about 3 millibars (~45 km) to the Earth's surface. At each channel frequency, the antenna beamwidth is a constant 3.3 degrees (at the half power point). Thirty contiguous scene resolution cells are sampled in a stepped-scan fashion every eight seconds with each scan covering 50 degrees on each side of the subsatellite path. The scan pattern and geometric resolution translate to a 50 km diameter cell at nadir and a 2,343 km swath width from the 833 km nominal orbital altitude. The AMSU-A system is implemented in two separate modules: the AMSU-A1 and AMSU-A2. AMSU-A1 consists of 12 V-band channels (3 through 14) and one W-band channel (15). This module provides a complete and accurate vertical temperature profile of the atmosphere from the Earth's surface to a height of approximately 45 km. AMSU-A2 contains the two lower frequencies (K-band channel 1 and Ka-band channel 2). This module is used to study atmospheric water in all of its forms with the exception of small ice particles. Summary of Parameters: Parameter Value -------------------------------------------------------------- Calibration Internal target and space background Channels 15 Cross-track scan angle +/- 48.33 degrees Scan time 8.0 seconds Number of steps 30 Step angle 3.33 degrees Step time 202.5 milliseconds Data precision 16 bits Time between start of each scan 8.0 seconds Angular FOV 3.33 degrees At an altitude of 833 km: Parameter Value -------------------------------------------------------------- Ground IFOV at Nadir 48.05 km diameter Ground IFOV at Center of Outer FOV 149.1 km cross-track by 79.4 km along-track Swath width 2,226.8 km to far edge of outer FOV AMSU-A Applications The AMSU-A instrument is part of the NOAA sounding instrument suite which was changed significantly starting with the NOAA-15 satellite. The four-channel MSU instrument was replaced by the 20-channel AMSU instrument suite, made up of AMSU-A for temperature and moisture and AMSU-B for moisture. In addition, AMSU-A essentially replaced the function of the SSU instrument. ATOVS uses the HIRS/3 and AMSU-A to generate the retrieved profiles. The AVHRR instrument is used for cloud detection along with the HIRS/3 and AMSU-A. Primarily because of resource limitations, the AMSU-B instrument is currently not part of the ATOVS system. A slightly modified version of the software developed and used to process the SSM/T-2 on the DMSP satellites is used to process the AMSU-B. The AMSU-B system became operational about one year after ATOVS because of satellite antenna interference in the AMSU-B data. Specifically, the AMSU-A is used for measuring global atmospheric temperature profiles and for gathering information on atmospheric water in all of its forms, save small ice particles which are transparent at microwave frequencies. AMSU-A Data Acquisition and Description The NOAA ATOVS processing flow begins with sensor data receipt by the Command and Data Acquisition (CDA) stations where the data are re-broadcast via communications satellites to NOAA/NESDIS in Suitland, MD where they are processed. Earth location and calibration data are appended, but not applied, to the data as part of the Level 1b processing. The earth locations are computed for specific pixels using the data time corrected for clock drift, if any. Shortly after arriving at NOAA/NESDIS, the data are made available at the Comprehensive Large Array-data Stewardship System (CLASS). AMSU-A Spatial Coverage Global coverage is available for the AMSU-A data which have an Instantaneous Field of View (IFOV) of approximately 3.3 degrees. From an altitude of 833 kilometers, this translates into a ground IFOV encompassing an area of 48.05 kilometers in diameter at nadir on the Earth. At scan end, a 149.1 km cross-track by 79.4 km along-track footprint is registered, again assuming a nominal altitude of 833 km. At the equator, the 96.66 degree scan equates to a swath width of 2,226.8 km to the far edge of the outer FOV centered on the subsatellite track. AMSU-A Temporal Coverage The overall coverage of the archived AMSU-A Level 1b data base is shown in the following table. However, associated with equipment malfunctions, there may be short gaps in the time ranges. Satellite Start Date End Date ------------------------------------- NOAA-15 10/26/98 Present NOAA-16 01/24/01 Present NOAA-17 06/28/02 Present AMSU-A Calibration The instrument is automatically calibrated each data cycle by measuring both warm and cold calibration targets. Once every 8 seconds, the AMSU-A measures 30 Earth views, the space view twice and the internal blackbody target twice. Additional information on the calibration of the AMSU-A may be found at: http://www2.ncdc.noaa.gov/docs/klm/html/c7/sec7-3.htm. AMSU-A Comprehensive Information Additional information on the AMSU-A sensor can be found in the NOAA KLM User's Guide at: http://www2.ncdc.noaa.gov/docs/klm/html/c3/sec3-3.htm. Details of the AMSU-A data sets can be found in the NOAA KLM User's Guide at: http://www2.ncdc.noaa.gov/docs/klm/html/c8/s831-6.htm. AMSU-B Introduction The Advanced Microwave Sounding Unit-B (AMSU-B) is a 5 channel microwave radiometer. The purpose of the instrument is to receive and measure radiation from a number of different layers of the atmosphere in order to obtain global data on humidity profiles. It works in conjunction with the AMSU-A instruments to provide a 20 channel microwave radiometer. AMSU-B covers channels 16 through 20. Channels 18, 19 and 20 span the strongly opaque water vapor absorption line at 183 GHz to provide data on the atmosphere's humidity level. Channels 16 and 17, at 89 GHz and 150 GHz, respectively, penetrate through the atmosphere to the Earth's surface. AMSU-B is a cross-track, line scanned instrument designed to measure scene radiances in 5 channels. At each channel frequency, the antenna beamwidth is a constant 1.1 degrees (at the half power point). Ninety contiguous scene resolution cells are sampled in a continuous fashion. Each scan covers roughly 50 degrees on each side of the subsatellite path. The scan pattern and geometric resolution translate to a 16.0 km diameter cell at nadir at a nominal altitude of 833 km. Summary of Parameters: Parameter Value ----------------------------------------------------------------- Calibration Internal target and space background Channels 5 Cross-track scan angle +/- 48.95 degrees Scan time 2.67 seconds Number of steps 90 Step angle 1.1 degrees Step time 19 milliseconds Data precision 16 bits Time between start of each scan 2.67 seconds Angular FOV 1.1 degrees At an altitude of 833 km: Parameter Value ------------------------------------------------------------------- Ground IFOV at Nadir 16.0 km diameter Ground IFOV at Center of Outer FOV 51.6 km cross-track by 26.9 km along-track Swath width 2,178.8 km to far edge of outer FOV AMSU-B Applications The AMSU-B instrument is part of the NOAA sounding instrument suite which was changed significantly starting with the NOAA-15 satellite. The four-channel MSU instrument was replaced by the 20-channel AMSU instrument suite, made up of AMSU-A for temperature and moisture and AMSU-B for moisture. In addition, AMSU-A essentially replaced the function of the SSU instrument. ATOVS uses the HIRS/3 and AMSU-A to generate the retrieved profiles. The AVHRR instrument is used for cloud detection along with the HIRS/3 and AMSU-A. Primarily because of resource limitations, the AMSU-B instrument is currently not part of the ATOVS system. A slightly modified version of the software developed and used to process the SSM/T-2 on the DMSP satellites is used to process the AMSU-B. The AMSU-B system became operational about one year after ATOVS because of satellite antenna interference in the AMSU-B data. The overall purpose of AMSU-B is to receive and measure radiation from a number of different layers within the atmosphere in order to obtain global data on humidity profiles. AMSU-B Data Acquisition and Description The NOAA ATOVS processing flow begins with sensor data receipt by the Command and Data Acquisition (CDA) stations where the data are re-broadcast via communications satellites to NOAA/NESDIS in Suitland, MD where they are processed. Earth location and calibration data are appended, but not applied, to the data as part of the Level 1b processing. The earth locations are computed for specific pixels using the data time corrected for clock drift, if any. Shortly after arriving at NOAA/NESDIS, the data are made available at the Comprehensive Large Array-data Stewardship System (CLASS). AMSU-B Spatial Coverage Global coverage is available for the AMSU-B data which have an Instantaneous Field of View (IFOV) of approximately 1.1 degrees. From an altitude of 833 kilometers, this translates into a ground IFOV encompassing an area of 16.0 kilometers in diameter at nadir on the Earth. At scan end, a 51.6 km cross-track by 26.9 km along-track footprint is registered, again assuming a nominal altitude of 833 km. At the equator, the 97.9 degree scan equates to a swath width of 2,178.8 km to the far edge of the outer FOV centered on the subsatellite track. AMSU-B Temporal Coverage The overall coverage of the archived AMSU-B Level 1b data base is shown in the following table. However, associated with equipment malfunctions, there may be short gaps in the time ranges. Satellite Start Date End Date --------------------------------------- NOAA-15 10/26/98 Present NOAA-16 01/24/01 Present NOAA-17 06/25/02 Present AMSU-B Calibration The instrument is automatically calibrated each data cycle by measuring both warm and cold calibration targets. Once every 8/3 seconds, the AMSU-B measures 90 Earth views, four space views and four internal blackbody target views. Information on the calibration of the AMSU-B may be found at: http://www2.ncdc.noaa.gov/docs/klm/html/c7/sec7-3.htm. AMSU-B Comprehensive Information Additional information on the AMSU-B sensor can be found in the NOAA KLM User's Guide at: http://www2.ncdc.noaa.gov/docs/klm/html/c3/sec3-4.htm. Details of the AMSU-B data sets can be found in the NOAA KLM User's Guide at: http://www2.ncdc.noaa.gov/docs/klm/html/c8/s831-7.htm. 3.4 Format These data are in level1b format. For details on this format see: http://www2.ncdc.noaa.gov/docs/klm/html/c8/s831-3.htm 4.0 Quality Control Procedures NCAR/EOL conducted no quality checks on these data. 5.0 File Naming Convention The file names are structured as follows: NSS.AMAX.NK.D04153.S0019.E0030.B3144949.WI.L8208391 Where AMAX signifies AMSU-A data and AMBX signifies AMSU-B data. NK is the satellite: NK = NOAA-15 NL = NOAA-16 NM = NOAA-17 D04153 signifies Year 2004 Julian Day 153 S0019 says the pass has a start time of 0019 UTC E0030 says the pass has an end time of 0030 UTC 6.0 References NOAA CLASS help system: http://www.class.noaa.gov/edna_help/systemhelp.htm