EPIC Satellite: NOAA POES HIRS Data 1.0 General Information The NOAA POES HIRS 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 East Pacific Investigation of Climate Processes in the Coupled Ocean-Atmosphere System (EPIC 2001) project. Included in the data set are measurements from the High Resolution Infrared Radiation Sounder (HIRS) system aboard the National Oceanic and Atmospheric Administration (NOAA) Polar Orbiting Environmental Satellites (POES). The data cover the period from 7 September - 28 October 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 EPIC region (20S-20N and 90-120W) are included within this data set. 2.0 Data Contact Steve Williams (sfw@ucar.edu) 3.0 Data and Format Information 3.1 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) replaces the MSU and the SSU, while the High Resolution Infrared Radiation Sounder Version 3 (HIRS/3) replaces the HIRS/2. ATOVS is slated to start using the Advanced Microwave Sounding Unit-B (AMSU-B) in the near future. 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 TOVS system can be found in the NOAA POD Guide located at: http://www2.ncdc.noaa.gov/docs/podug/index.htm 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 HIRS/2 Information 3.2.1 Introduction The High Resolution Infrared Radiation Sounder Version 2 (HIRS/2) is part of the TOVS instrument suite flown onboard the TIROS-N and NOAA 6 through NOAA 14 satellites. The HIRS/2 is a step-scanned multi-channel spectrometer with 20 channels, 19 of which are in the infrared region of the spectrum with the remaining channel in the visible region. The HIRS/2 Level 1b data include 13 bit precision data values from these 20 spectral channels. The visible data values (Channel 20) may be converted into albedos and the IR data (Channels 1-19) may be converted into brightness temperatures using the calibration information which is appended but not applied to each scan line. Latitudes and longitudes for each of the 56 Earth FOVs in each scan are included as are time tags. Summary of Parameters: Parameter Value -------------------------------------------------------------------- Calibration Stable blackbodies (2) 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 rate 2,880 bits/second Data precision 13 bits Time between start of each scan 6.4 seconds Angular FOV 1.25 degrees At an altitude of 833 km: Parameter Value -------------------------------------------------------------------- Ground IFOV at Nadir 17.7 km diameter Ground IFOV (end of scan) 59.5 km cross-track by 30.4 km along-track Distance between IFOV centers 42.0 km along-track Swath width (to far edge of outer FOV) 2,239.6 km 3.2.2 HIRS/2 Applications In addition to profiles of temperature and moisture, the HIRS/2 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. 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. 3.2.3 HIRS/2 Data Acquisition and Description The NOAA TOVS 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. The ephemeris data (orbital reference information) are funneled through the Advanced Earth Location Data System (AELDS) software. 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 HIRS/2 Spatial Coverage Global coverage is available for the HIRS/2 data which have an Instantaneous Field of View (IFOV) with a 17.7 km diameter at nadir and a 59.5 km cross track by 30.4 km along-track footprint at the end of the scan, assuming a nominal altitude of 833 km. The HIRS/2 instrument provides a global (pole-to-pole) on-board collection of data from all 20 spectral channels. The 99 degree scan equates to a swath width of 2239.6 km (at the Equator) centered on the subsatellite track. As a result of the scan geometry, there is variable underlap between steps and scans. 3.2.5 HIRS/2 Calibration The HIRS/2 sensor can be commanded to automatically enter a calibration mode every 256 seconds. When the instrument is in the calibration mode, the mirror (starting from the beginning of a scan line) rapidly slews to a space view and samples all channels for the equivalent time of one complete scan line of 56 scan steps. Next, the mirror is moved to a position where it views a cold calibration target and data are taken for the equivalent of 56 scan steps. The mirror is then stepped to view an internal warm target for another 56 scan steps. Upon completion of the HIRS/2 calibration mode, the mirror continues its motion to the home position where it begins normal Earth scan. The total calibration sequence is equivalent to three scan lines (no Earth location data are obtained during this period). Additional calibration information may be found at: http://www2.ncdc.noaa.gov/docs/podug/html/c4/sec4-5.htm 3.2.6 HIRS/2 Comprehensive Information Additional information on the HIRS/2 can be found in the NOAA Polar Orbiter Data User's Guide at: http://www2.ncdc.noaa.gov/docs/podug/html/c4/sec4-1.htm 3.3 HIRS/3 Information 3.3.1 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 3.3.2 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. 3.3.3 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 Satellite Active Archive (SAA). 3.3.4 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. 3.3.5 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. 3.3.6 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/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.HIRX.NJ.D01187.S1301.E1434.B3358687.GC.L1306957 Where HIRX signifies HIRS data NL is the satellite: NJ = NOAA-14 NK = NOAA-15 NL = NOAA-16 D01187 signifies Year 2001 Julian Day 187 S1301 says the pass has a start time of 1301 UTC E1434 says the pass has an end time of 1434 UTC 6.0 References None