NAME Satellite: NOAA POES HIRS/3 Data (level 1b) 1.0 General Information The NOAA POES ATOVS HIRS/3 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) High Resolution Infrared Radiation Sounder Version 3 (HIRS/3) 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. HIRS/3 Introduction The High Resolution Infrared Radiation Sounder (HIRS/3) is part of the ATOVS instrument suite flown onboard the NOAA KLM series of satellites. The HIRS/3 is a discrete stepping, line-scan instrument designed to measure scene radiance in 20 spectral bands to permit the calculation of the vertical temperature profile from the Earth's surface to about 40 km. Multispectral data from one visible channel (0.69 micrometers), seven shortwave channels (3.7 to 4.6 micrometers) and twelve longwave channels (6.5 to 15 micrometers) are obtained from a single telescope and a rotating filter wheel containing twenty individual filters. An elliptical scan mirror provides cross-track scanning of 56 increments of 1.8 degrees. The mirror steps rapidly (<35 msec), then holds at each position while the 20 filter segments are sampled. This action takes place each 100 msec. The instantaneous FOV for each channel is approximately 1.4 degrees in the visible and shortwave IR and 1.3 degrees in the longwave IR band which, from an altitude of 833 kilometers, encompasses an area of 20.3 kilometers and 18.9 kilometers in diameter, respectively, at nadir on the Earth. Summary of Parameters Parameter Value ----------------------------------------------------------- IR Calibration Warm target and space background Channels 20 Cross-track scan angle +/- 49.5 degrees Scan time 6.4 seconds Number of steps 56 Step angle 1.8 degrees Step time 100 milliseconds Data precision 13 bits Time between start of each scan 6.4 seconds Angular FOV (visible, shortwave IR) 1.40 degrees Angular FOV (longwave IR) 1.30 degrees At an altitude of 833 km: Parameter Value ------------------------------------------------------------ Nadir Ground IFOV (visible, shortwave IR) 20.3 km diameter Nadir Ground IFOV (longwave IR) 18.9 km diameter Scan-end Ground IFOV (visible, shortwave) 68.3 km cross-track by 34.8 km along-track Swath width (visible, shortwave IR) 2,248.8 km to far edge of outer FOV HIRS/3 Applications In addition to profiles of temperature and moisture, the HIRS/3 data are used for a diverse range of applications including the derivation of surface skin temperature, sea surface temperature, outgoing longwave radiation, cloud fraction, cloud-top height, total integrated column ozone, precipitation estimates, and wind speed and direction. The HIRS/3 instrument is used as 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. HIRS/3 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). HIRS/3 Spatial Coverage Global coverage is available for the HIRS/3 data which have an Instantaneous Field of View (IFOV) of approximately 1.4 degrees in the visible and shortwave IR and 1.3 degrees in the longwave IR band. From an altitude of 833 kilometers, these translate into a ground IFOV encompassing an area of 20.3 kilometers and 18.9 kilometers in diameter, respectively, at nadir on the Earth. At scan end, a 68.3 km cross-track by 34.8 km along-track footprint is registered for the visible and shortwave IR channels, again assuming a nominal altitude of 833 km. The HIRS/3 instrument provides a global (pole-to-pole) on-board collection of data from all 20 spectral channels. At the equator, the 99 degree scan equates to a swath width of 2,248.8 km to the far edge of the outer FOV centered on the subsatellite track. As a result of the scan geometry, there is variable underlap between steps and scans. HIRS/3 Temporal Coverage The overall coverage of the archived HIRS/3 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 02/26/01 Present NOAA-17 07/10/02 Present HIRS/3 Calibration Information on the calibration of the HIRS/3 may be found at: http://www2.ncdc.noaa.gov/docs/klm/html/c7/sec7-2.htm. HIRS/3 Comprehensive Information Additional information on the HIRS/3 sensor can be found in the NOAA KLM User's Guide at: http://www2.ncdc.noaa.gov/docs/klm/html/c3/sec3-2.htm. Details of the HIRS/3 data sets can be found in the NOAA KLM User's Guide at: http://www2.ncdc.noaa.gov/docs/klm/html/c8/s831-5.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.HIRX.NK.D04153.S0019.E0030.B3144949.WI.L8208391 Where HIRX signifies HIRS/3 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