DYCOMS-II Satellite: NOAA POES AMSUB Data 1.0 General Information The NOAA POES AMSUB Data is one of several satellite data sets collected by the University Corporation for Atmospheric Research/Joint Office for Science Support (UCAR/JOSS) as part of the Dynamics and Chemistry of Marine Stratocumulus Phase II: Entrainment Studies (DYCOMS-II) project. Included in the data set are measurements from the Advanced Microwave Sounding Unit-B (AMSU-B) system aboard the National Oceanic and Atmospheric Administration (NOAA) Polar Orbiting Environmental Satellites (POES). The data cover the period from 7 - 28 July 2001. Data are available at POES satellite overpass times. These data were acquired from the NOAA Satellite Active Archive (http://www.saa.noaa.gov) and are in level1B format. Any passes that had any portion over the DYCOMS-II region (26-37N and 115- 127W) are included within this data set. 2.0 Data Contact Scot Loehrer (loehrer@ucar.edu) 3.0 Data and Format Information 3.1 ATOVS Introduction In the Advanced TIROS Operational Vertical Sounder (ATOVS) system, the Advanced Microwave Sounding Unit-A (AMSU-A) replaces the Microwave Sounding Unit (MSU) and the Stratospheric Sounding Unit (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 currently fields NOAA 15 and NOAA 16. Each instrument has different characteristics, resolutions, scan properties, etc. which are described below. Detailed information on the ATOVS system can be found in the NOAA KLM User's Guide located at: http://www2.ncdc.noaa.gov/docs/klm/index.htm 3.2 AMSU-B Information 3.2.1 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 3.2.2 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. 3.2.3 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 Satellite Active Archive (SAA). 3.2.4 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. 3.2.5 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. 3.2.6 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. 3.2.7 Format These data are in level1b format. For details on this format see: http://www2.ncdc.noaa.gov/docs/klm/html/c8/s8-0.htm 4.0 Quality Control Procedures UCAR/JOSS conducted no quality checks on these data. 5.0 File Naming Convention The file names are structured as follows: NSS.AMBX.NL.D01204.S2110.E2257.B0430809.GC.L1347572 Where AMBX signifies AMSU-B data NL is the satellite: NJ = NOAA-14 NK = NOAA-15 NL = NOAA-16 D01204 signifies Year 2001 Julian Day 204 S2110 says the pass has a start time of 2110 UTC E2257 says the pass has an end time of 2257 UTC 6.0 References None