DYCOMS-II Satellite: NOAA POES SSU Data 1.0 General Information The NOAA POES SSU 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 Stratospheric Sounding Unit (SSU) system which is part of the TIROS Operational Vertical Sounder (TOVS) instrument suite aboard the National Oceanic and Atmospheric Administration (NOAA) Polar Orbiting Environmental Satellites (POES). The data cover the period from 11 - 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 TOVS 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. 3.2 SSU Information 3.2.1 Introduction The Stratospheric Sounding Unit (SSU) is part of the TOVS instrument suite flown onboard the TIROS-N and NOAA 6 through NOAA 14 satellites. The SSU is a step-scanned infrared spectrometer employing a selective absorption technique to make measurements at the top of the Earth's atmosphere in three channels in the 15 micron carbon dioxide absorption band. The three SSU channels have the same frequency but different cell pressures. The 10.0 degree angular Instantaneous Field of View (IFOV) gives a resolution of 147.3 km at nadir. The distance between adjacent scan lines is 62.3 km at nadir. Data are from three channels at 12 bit precision and may be converted into brightness temperatures using the calibration information which is appended but not applied. Latitudes and longitudes for each of the eight Earth FOVs in each scan are included as are time tags. Summary of Parameters: Parameter Value ---------------------------------------------------------------- Calibration Stable blackbody and space Channels 3 Cross-track scan angle +/- 40.0 degrees from nadir Scan time 32.0 seconds Number of Earth views/line 8 Step angle 10.0 degrees Step time 4.0 seconds Data rate 480 bits per second Data precision 12 bits Time between start of each scan 32 seconds Angular field of view 10.0 degrees At an altitude of 833 km: Parameter Value ------------------------------------------------------------------ Ground IFOV (nadir) 147.3 km diameter Ground IFOV (end of scan) 244.0 km cross-track by 186.1 km along-track Distance between IFOV centers 62.3 km along-track Swath width 1,474 km 3.2.2 SSU Applications The primary objective of the SSU instrument is to obtain data from which stratospheric (~25-50 km) temperature profiles can be determined. 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. Satellite observations have been very valuable for establishing the climatology and phenomenology of large scale waves, especially the propagation of Rosby waves in the mid-latitudes. With satellite data, the mean zonal and temporal structures of stratospheric disturbances can be defined and their slow, large-scale variations can be resolved. The general circulation in the stratosphere can be defined largely in terms of radiative forcing and dynamical interaction between large-scale, slowly varying waves and the mean zonal flow. 3.2.3 SSU 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 SSU Spatial Coverage The cross-track scan of the SSU instrument, combined with the satellite's motion in orbit, provides coverage of a major portion of the Earth's surface. The SSU instrument provides a nearly global (pole-to-pole) on-board collection of data from all three spectral channels. The SSU antennas scan 40.0 degrees on either side of nadir in eight steps. Assuming a nominal altitude of 833 km, the angular Field of View (FOV) of 10.0 degrees results in a ground resolution at the subpoint of 147.3 km diameter, while the IFOV at the end of the scan is 244.0 km cross-track by 186.1 km along-track. The swath width is 1,474 km (at the Equator) centered on the subsatellite track. At nadir, 62.3 km separate consecutive scan lines. 3.2.5 SSU Calibration A calibration sequence is initiated every 256 seconds (eight scans) during which the radiometer is, in turn, stepped to view unobstructed space and then to view an internal blackbody of a known temperature. This mode is synchronized with the HIRS/2 instrument. Additional calibration information may be found at: http://www2.ncdc.noaa.gov/docs/podug/html/c4/sec4-5.htm 3.2.6 SSU Comprehensive Information Additional information on the SSU can be found in the NOAA Polar Orbiter Data User's Guide at: http://www2.ncdc.noaa.gov/docs/podug/html/c4/sec4-2.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.SSUX.NJ.D01200.S1354.E1519.B3377071.GC.L1336930 Where SSUX signifies SSU data NJ is the satellite: NJ = NOAA-14 D01200 signifies Year 2001 Julian Day 200 S1354 says the pass has a start time of 1354 UTC E1519 says the pass has an end time of 1519 UTC 6.0 References None