DYCOMS-II Satellite: NOAA POES AMSUA Data 1.0 General Information The NOAA POES AMSUA 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-A (AMSU-A) 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-A Information 3.2.1 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 3.2.2 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. 3.2.3 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 Satellite Active Archive (SAA). 3.2.4 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. 3.2.5 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. 3.2.6 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. 3.2.6 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.AMAX.NL.D01202.S2131.E2318.B0428081.GC.L1343032 Where AMAX signifies AMSU-A data NL is the satellite: NJ = NOAA-14 NK = NOAA-15 NL = NOAA-16 D01202 signifies Year 2001 Julian Day 202 S2131 says the pass has a start time of 2131 UTC E2318 says the pass has an end time of 2318 UTC 6.0 References None