DYCOMS-II Satellite: NOAA POES MSU Data 1.0 General Information The NOAA POES MSU 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 Microwave Sounding Unit (MSU) 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 MSU Information 3.2.1 Introduction The Microwave Sounding Unit (MSU) is part of the TOVS instrument suite flown onboard the TIROS_N and NOAA 6 through NOAA 14 satellites. The MSU is a passive scanning microwave spectrometer with four channels in the 5.5 micron oxygen region. The MSU consists of two four-inch diameter antennas, each having an angular Instantaneous Field of View (IFOV) of 7.5 degrees. Assuming a nominal altitude of 833 km, ground resolution is 124 km at the subpoint, while the distance between adjacent scan lines is 168.1 km at nadir. Data from the four channels are 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 Earth FOVs in each scan are included as are time tags. Users wanting MSU data on-line may specify only whole data sets through the Satellite Active Archive since, at this time, there is no select capability available for MSU data. Summary of Parameters: Parameter Value ---------------------------------------------------------------- Calibration Hot reference body and space background each scan cycle Channels 4 Cross-track scan angle +/- 47.35 degrees Scan time 25.6 seconds Number of steps 11 Step angle 9.47 degrees Step time 1.84 seconds Data rate 320 bits/second Data precision 12 bits Time between start of each scan 25.6 seconds Angular field of view 7.5 degrees (3 dB) At an altitude of 833 km: Parameter Value Ground IFOV (nadir) 109.3 km diameter Ground IFOV (end of scan) 323.1 km cross-track by 178.8 km along-track Distance between IFOV centers 168.1 km along-track Swath width 2,348 km 3.2.2 MSU Applications Because the longer wavelengths of microwaves can penetrate most cloud systems, observations of thermal emission in the microwave region can provide temperatures below clouds. Interpretation of microwave observations is hampered by surface emissivity effects and sensitivity to precipitation. But these mechanisms also open possibilities for sensing precipitation as well as surface properties such as snow, sea ice, and soil moisture. 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 MSU 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 MSU Spatial Coverage The MSU provides a global (pole-to-pole) on-board collection of data from all four spectral channels. The two four-inch diameter MSU antennas scan 47.35 degrees on either side of nadir in 11 steps. Assuming a nominal altitude of 833 km, the 7.5 degree antenna beamwidth results in a ground resolution at the subpoint of 109.3 km, while the Instantaneous Field of View at the end of the scan is 323.1 km cross-track by 178.8 km along-track. The swath width is 2,348 km, while the resolution at the subpoint creates an underlap of 115 km between adjacent scan lines. 3.2.5 MSU Calibration Unlike the HIRS/2 and SSU instruments, the MSU has no special calibration sequence that interrupts normal scanning. The calibration data are included in a scan line of data. From the last Earth view position, the reflector rapidly moves four steps to view space, 10 additional steps to view the housing, and then returns to the home position to begin another scan line. Since each scan line requires 25.6 seconds, synchronization of MSU within the other two TOVS instruments occurs every 128 seconds (5 scan lines). Additional calibration information may be found at: http://www2.ncdc.noaa.gov/docs/podug/html/c4/sec4-5.htm 3.2.6 MSU Comprehensive Information Additional information on the MSU can be found in the NOAA Polar Orbiter Data User's Guide at: http://www2.ncdc.noaa.gov/docs/podug/html/c4/sec4-3.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.MSUX.NJ.D01195.S1306.E1500.B3369900.GC.L1325299 Where MSUX signifies MSU data (the NOAA-12 data has MSUS) NJ is the satellite: ND = NOAA-12 NJ = NOAA-14 NK = NOAA-15 NL = NOAA-16 D01195 signifies Year 2001 Julian Day 195 S1306 says the pass has a start time of 1306 UTC E1500 says the pass has an end time of 1500 UTC 6.0 References None