NASA Reference Publication 1221 1989 Nimbus-7 Stratospheric and Mesospheric Sounder (SAMs) Experiment Data User’s Guide F. W. Taylor and C. D. Rodgers University of Oxford Oxford, England S. T. Nutter and N. Os& ST Systems Corporation (STX) Lanham, Maryland National Aeronautics and Space Administration Off ice of Management Scientific and Technical Information Division FOREWORD ;-7 Stratospheric and Mesospheric Sounder (SAMs) Experiment Data User's Guide is intended to provide Immunity with the background information necessary for understanding and using data products on SAMS lred Temperature Tapes (GRID-T), and Zonal Mean Methane and Nitrous Oxide Tapes (ZMT-G). The :nt was flown aboard the Nimbus-7 spacecraft and collected data from October 26, 1978 through June 9, ument provides users with information concerning the operational principles of the SAMs instrument and the retrieval of temperature and atmospheric constituents, and the scientific validity of SAMS data. nts that influence the quality of data are included along with the mission history. Data formats of the MT-G tape products and descriptions of SAMS data are also given. al discussion in this document was prepared originally by the SAMS processing team at Oxford, England. nvestigator was Dr. F. W. Taylor and the NET chairman was Dr. C. D. Rodgers. All questions of a 5 should be addressed to these individuals, at the address given in Section 1.5. The description of the tape ed upon the data tapes provided for conversion from the DEC format available from Oxford to the IBM I by the Nimbus project. The text provided by the SAMs processing team and the information gained from the data tapes were compiled into this document for NASA by S. T. Nutter and N. Oslik of ST Systems IX) under contract NAS5-28063. PRECEDING PAGE BLANK NOT FILMED ... 111 ,* II JNrE-m ~~ TABLE OF CONTENTS Section ... FOREWORD., ..................................... 111 1 PURPOSE. INTRODUCTION. AND OBJECTIVES ....................1 1.1 Purpose of the Data User's Guide ........................ 1 1.2 Introduction. ................................. 1 1.3 Objectives ................................... 2 1.4 DataROducts ................................. 2 1.5 Principal Investigators ............................. 3 2 INSTRUMENT DESCRIPTION .............................. 5 3 DATA PROCESSING ................................... 7 3.1 Calibration ................................... 7 3.2 Retrieval of Temperature and Constituents ...................10 3.3 SAMS Temperature Gridding .........................11 VALIDATION ....................................... 13 MISSION HISTORY AND CHANNEL STATUS ..................... 15 DATA FORMATS ..................................... 49 6.1 Format of SAMS Gridded Retrieved Temperature Tapes (GRID-T) ................................ 49 6.2 Format of SAMs Zonal Mean Methane and Nitrous Oxide Composition Tape (ZMT-G) .......................... 61 REFERENCES ..............................................67 LIST OF ACRONYMS. INITIALS. AND ABBREVIATIONS ......................69 Amendixes A SEQUENCE NUMBERS OF SAMs DATA TAPES .................... 71 B FORTRAN SOURCE LISTING OF SAMS TAPE DUMP .................73 C STRATOSPHERIC AND MESOSPHERIC SOUNDER ON NIMBUS-7 ..........89 D RETRIEVAL OF TEMPERATURE AND COMPOSITION FROM NIMBUS-7 SAMs MEASUREMENTS .......................... 113 E TEMPERATURE COMPARISONS BETWEEN THE NIMBUS-7 SAMS. ROCKEiT/RADIOSONDES AND THE NOAA 6 SSU .................. 121 F OBSERVATIONS OF CHq AND N20 BY THE NIMBUS-7 SAMS: A C0I"ARISON WITH IN SITU DATA AND TWO-DIMENSIONAL NUMERICAL MODEL CALCULATIONS ........................ 131 G SOME ASPECTS OF THE DESIGN AND BEHAVIOR OF THE STRATOSPHERIC AND MESOSPHERIC SOUNDER ...............149 V SECTION 1 PURPOSE, INTRODUCTION, AND OBJECTIVES 1.1 Purpose of the Data User's Guide The SAMs Data User's Guide is intended to provide the scientific community wit. the background information needed to access data on SAMs GRID-T and ZMT-G tapes. The document describes the SAMs instrument, the method of temperature and constituent retrieval, data calibration, and data validation. Section 1 of this document explains the scientific and technical objectives of the SAMs instrument. Section 2 briefly discusses the literature from which a description of the instrument can be obtained. Reprints of two relevant papers appear as Appendixes C and G to this User's Guide. Section 3 outlines the data processing system, explains instrument calibration, briefly describes the temperature and constituent remeval process, and explains the temperature gridding procedure. Section 4, like Section 2, provides an introduction to literature that discusses the accuracy of the retrievals and compares the SAMs results with those of other measurements. Reprints of two relevant papers are included as Appendixes E and F of this User's Guide. Important dates in the history of the SAMs instrument and information concerning the status of SAMs channels are given in Section 5. The data formats of the SAMs GRID-T and ZMT-G tapes are described in detail in Section 6. A FORTRAN source listing of a SAMs tape dump program is included in Appendix B. This program enables users to access data on GRID-T and ZMT-G tapes. 1.2 Introduction The Stratospheric and Mesospheric Sounder (SAMs) instrument flown on Nimbus-7 is the fourth in a series of multi-channel infrared radiometers designed to measure emission from the upper atmosphere, for which conventional spectral filtering techniques do not give adequate performance. The technique used in these radiometers is known as gas correlation spectroscopy and is based on the use of gas cells to select emission from chosen spectral lines or from particular parts of spectral lines. In the Selective Chopper Radiometer (SCR) on Nimbus-4, a beamchopping technique was employed to switch the scene (at 10 Hz) between the atmosphere and space view in a differential manner between two gas cells containing different amounts of C@. The "difference" signal was then detected by a thermistor bolometer. The chief limitation in performance of the Nimbus4 SCR was the difficulty in maintaining a balance condition due to stray thermal emission from within the instrument. Nimbus-5 employed a variation of this technique, in which cells containing different amounts of C02 were switched in sequence (one each second) into the optical path to a pyroelectric detector. The difference signals were then extracted on the ground. Performance in this case was limited by gas leakage with time, by uncertainties in the effects of degradation, and by contamination of the cell windows (which give spurious difference signals). The Pressure Modulator Radiometer (PMR) on Nimbus-6 overcame earlier difficulties by employing a single gas cell and no moving parts in front of the detector. The gas (C02) amount in the cell is modulated at approximately 35 Hz by an oscillating piston, and the oscillatory component of the signal arriving at the detector is related directly to the radiance of the scene, but only at the frequencies corresponding to the variation in absorption of the spectral lines of the gas in the modulator cell. The SAMs instrument views the limb of the atmosphere, rather than employing vertical sounding as in the earlier radiometers. The technique has been extended to gases other than CW. 1.3 Objectives The SAMs is a 12-channel infrared radiometer observing thermal emission and solar resonance fluorescence from the atmospheric limb. Global measurements are made of radiation from the molecular species listed in Table 1-1. These measurements, when interpreted together with results from the LIMS and SBUV/rOMS instruments, provide extensive data for chemical and dynamical models of the stratosphere and mesosphere. Specific objectives of the SAMs experiment were to derive the following quantities: a) Temperature for altitudes from 15 km to 80 km, from emission in the 15 pm C02 band. b) Vibrational temperature of C02 bands where they depart from local thermodynamic equilibrium (LTE),between 50 km and 140 km. c) Distributions of CO, NO, CHq, N20, and H20 from 15 km to 60 km. d) Distributions of C02 (4.3 pm) from 100 km to 140 km and H20 from 60 km to 100 km, to study dissociation in the lower thermosphere. The study of planetary waves that used data from the Nimbus-5 SCR and Nimbus-6 PMR can be continued and extended by making use of these new data. In addition, the measurements allow calculation of the transfer of momentum, energy, and trace gases by mean motions and eddies. The SAMs instrument is designed to exploit the selectivity, energy grasp, and tuning capability of the pressure modulation technique proved earlier for C02 emission measurements in he Nimbus-6 PMR (Curtis et a1.,1974). The main technical innovations in SAMs are as follows: a) The extension of the pressure modulation technique to other gases. b) The simultaneous use of conventional chopping and pressure modulation to 1) Extend the range of heights that can be sounded 2) Determine the pressure at the viewing level 3) Enable some interfering radiance signals to be eliminated 4) Provide additional calibration information and confidence checks c) The use of a programmable scan system with two independent axes to optimize usage of the observing time and to accommodate uncertainties in spacecraft attitude. 1.4 Data Products Retrieved temperature and constituent information from the SAMs instrument is stored on two data products, GRID-T and ZMT-G tapes, respectively, which are archived at the National