Earth Radiation Budget Experiment (ERBE) Solar Monitor Irradiance Langley ASDC Data Set Document
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Earth Radiation Budget Experiment (ERBE) Solar Monitor Irradiance Langley ASDC Data Set Document |
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This document describes the Solar Monitor Irradiance data set and provides the user with the necessary information to use the Earth Radiation Budget Experiment (ERBE) data for scientific research studies.
The solar monitor channel of the nonscanner instrument measures the total output of radiant heat and light from the sun. The ERBE nonscanner solar calibrations are performed by commanding the elevation beam to the solar calibration position (i.e. solar ports) which allows the earth-viewing detector modules to view space just above the Earth's limb. The solar ports restrict the detectors from viewing the Earth or spacecraft structure and are aligned with the instrument head is then commended to rotate to the proper azimuth angle. The angle is determined from updated spacecraft ephemeris data and is stored in instrument memory prior to initiating the solar calibration sequence. Once the instrument is in position, the sun passes through the Earth detectors, SMA, and SAS fields-of-view.
The sequence of events associated with solar calibrations positions the instrument in elevation and azimuth, starts the SMA shutter cycle (32 second open - 32 seconds closed) and turns on the detector bias heaters. The solar monitor shutter enables more precise solar measurements to be obtained because the zero reference can be obtained 32 seconds before and after the sun-view. This automatic solar calibration sequence is initiated via a single ground system command issued 28 minutes and 48 seconds prior to the sun passing through the center of the instrument fields-of-view. The Earth-viewing channels are elevated to the solar-viewing position early in the sequence to allow them to be radiometrically "chopped" (referenced) against the absolute zero irradiance of space both before and after the solar viewing event. By taking advantage of this chopping in the data analysis, an exceptionally accurate solar measurement can be made.
During normal mission operations, the ERBE nonscanner instrument is positioned for solar-viewing approximately every 14 days. Beginning in late January, 1985 and continuing throughout the normal mission life of both spacecraft, solar observations are scheduled within one hour of each other for each respective spacecraft (ERBS, NOAA-9, and NOAA-10).
Earth Radiation Budget Experiment (ERBE) Total Solar Irradiance (from the Earth Radiation Budget Satellite (ERBS) in Native (NAT) Format (ERBE_TSI_ERBS_NAT), ERBE_TSI_ERBS_NAT)
See Summary.
The objectives of the ERBE solar monitors are:
The solar monitor channel of the nonscanner instrument collects about 20 minutes of usable data during solar calibration periods which may occur as often as once a week or during special periods daily. Out of these 20 minutes or so of data, between 1 to 4 irradiance values are computed and averaged giving one irradiance value per day. All of the data are ordered chronologically and contain the following:
The goal of the ERBE is to produce monthly averages of longwave and shortwave radiation parameters on the Earth at regional to global scales. Preflight mission analysis lead to a three-spacecraft system to provide the geographic and temporal sampling required to meet this goal. Three nearly identical sets of instruments were built and launched on three separate spacecraft. These instruments differ principally in the spacecraft interface electronics and in the field-of-view limiters for the nonscanner instruments required because of differences in the spacecraft orbit altitudes.
The ERBS spacecraft was launched by Space Shuttle Challenger in October 1984 and was the first spacecraft to carry ERBE instruments into orbit. The ERBS was designed and built by Ball Aerospace Systems under contract to NASA Goddard Space Flight Center (GSFC), and ERBS was the first spacecraft dedicated to NASA science experiments to be launched by the Space Shuttle. The ERBS carries the Stratospheric Aerosol and Gas Experiment II (SAGE II) in addition to the ERBE instruments. The Payload Operation and Control Center (POCC) at GSFC directs operations of the ERBS spacecraft and the ERBE and SAGE II instruments, employing both ground stations and the Tracking and Data Relay Satellite System (TDRSS) network. Spacecraft and instrument telemetry data are received at GSFC where the data are processed by the Information Processing Division that provides ERBE and SAGE II experiment tapes to the NASA Langley Research Center (LaRC).
NASA tracks the ERBS spacecraft. The tracking data are provided to GSFC where orbit ephemeris data are calculated and provided (on either magnetic tape or via Internet file transfer) to LaRC.
There are no data sets related to this data set.
Earth Radiation Budget Experiment (ERBE) Total Solar Irradiance
Mr. Robert S. Wilson
SAIC
One Enterprise Pkwy
Suite 250
Hampton, Virginia 23666
Telephone: (757) 827-4881
E-mail: r.s.wilson@larc.nasa.gov
Ms. Susan Thomas
SAIC
One Enterprise Pkwy
Suite 250
Hampton, Virginia 23666
Telephone: (757) 827-4881
E-mail: s.thomas@larc.nasa.gov
The theory behind the measurements made to collect the ERBE data is non-trivial and well beyond the scope of this document. However, interested readers are referred to Ref. 1.
The ERBE solar monitor instrument was designed to collect data for one year but had a goal of two years. The instrument continues to collect data.
The ERBS satellite was launched on October 5, 1984 into a precessing 57 degree inclined orbit with a semi-major axis of 6988 km and a mean altitude of 610 km with a 98 minute nodal period.
The Solar monitor instrument is on the ERBS satellite.
ERBS was the first spacecraft dedicated to NASA science experiments to be launched by the Space Shuttle. ERBS carries SAGE II instruments in addition to the ERBE instruments.
Total Solar irradiance, Date, Time, Standard deviation
The ERBE is a multisatellite system designed to measure the Earth's radiation budget. The ERBE instruments fly on a mid-inclination NASA satellite, (ERBS). The satellite carries a nonscanner instrument package consisting of two channels which measure shortwave reflected radiances (0.2-5.0 microns) and three which measure the total wavelengths (0.2-50.0 microns) which includes the solar monitor.
The nonscanner instrument package contains four Earth-viewing channels and a solar monitor. The solar monitor is a direct descendant of the Solar Maximum Mission's Active Cavity Radiometer Irradiance Monitor detector. Because of the concern for spectral flatness and high accuracy, all five of the channels on the nonscanner package are active cavity radiometers.
The solar monitor assembly is fixed at at 78 degree solar calibration position.
The ERBE instruments were developed by TRW, Inc.
Not obtainable.
This information is not available.
In-flight solar calibrations of the nonscanners were normally performed on a bi-weekly basis. During periods of special operation (SOLCON experiment, ect) solar monitor calibrations were done as frequently as every day, for to 14 orbits.
The ERBE instruments were developed by TRW, Inc. Laboratory calibrations of the ERBE scanner, nonscanner, and solar monitor instruments were completed in the TRW calibration facility at Redondo Beach, California in 1984. The fundamental standards used for the ERBE instruments were the International Pressure and Temperature Standard of 1968 (IPTS-68) and the World Radiation Reference (WRR). The TRW master reference blackbody (MRBB) was calibrated using these, and the MRBB was subsequently used to transfer the calibrations to the internal blackbody (IBB) and to the shortwave channels via an integrating sphere. The results of the calibrations were reported in detail in TRW calibration documents.
In-flight calibrations are performed in order to maintain the accuracy of radiometric measurements by accounting for internal instrument component parametric changes brought about by the spacecraft's environmental variables. In-flight calibrations of the nonscanners were also normally performed on a bi-weekly basis. These included internal calibrations, space looks, and solar calibrations. Internal calibrations consist of cycling of IBB temperatures (total sensors) and shortwave internal calibration source (SWICS) voltages. Space looks consist of observations of "cold" space, both before and after solar calibrations. Solar calibrations consist of measurements made while the solar disc is within the instrument's FOV.
Each of the satellites carrying ERBE instruments carries a pair of instrument packages. The first package is a scanner instrument. The second instrument package is a nonscanner for obtaining large-scale Earth fluxes and solar irradiance measurements. The nonscanner has four Earth-viewing channels and a solar monitor. Observations of the sun check the stability and precision of the instruments while in flight.
Not obtainable.
Not obtainable.
Even though the Earth-viewing detectors have spatial coverage on the Earth, the solar monitor does not view the Earth at any time.
This information is not available.
The solar monitor instrument has an unencumbered FOV which observes the entire solar disk during solar observation periods.
This information is not available.
This information is not applicable.
The solar instrument collects about 20 minutes of usable data during bi-weekly solar calibration periods.
The solar data results in the computation of from 1 to 3 solar irradiance values per 20 minutes of usable data which are averaged to produce a single irradiance value.
Total Solar Irradiance
In this section, each data item in a record is defined. Each definition begins with the "Record Index" and the parameter name. This heading is followed by a brief description of the parameter. The range of possible values is denoted by brackets. Some definitions are followed by notes which list more detailed information about the data item.
Date
Year/Month/Day
Time
The Time consists of the Hour:Minute:Second of the sun-view in the middle of the measurement cycle.
Total Solar irradiance (Watts/square meter)
The average power received on a unit area at the mean Earth/Sun distance.
Standard deviation (Watts/suare meter)
The standard deviation of from 1 to 4 irradiance values during the day.
Units of measurement for the calculated and measured science variables for the solar irradiance data product can be found in the Variable Description/Definition.
The solar monitor channel of the nonscanner collects about 20 minutes of usable data during solar calibration periods. The ERBS total solar irradiance product consists of the irradiance values computed from data taken during each solar calibration period of the day.
YR/MO/DY HR:MN:SC IRR STD 84/10/25 15:24:45 1364.8 0.1 84/10/26 10:44:49 1365.4 0.2 84/10/29 11:21:05 1365.2 0.0
A general description of data granularity as it applies to the IMS appears in the EOSDIS Glossary.
Each granule contains six months of data. There are also granules that consist of all data collected for this data set.
All data granules are in ASCII format.
There are a number of steps in the processing of the ERBE data. The mathematics involved in each of these steps is beyond the scope of this document. However, interested readers are referred to Reference 1.
The Langley Research Center (LaRC) has the responsibility of processing and validating all science data from the ERBE mission and of distributing the resulting data products to the science community. The ERBE data processing system at LaRC uses a modular software subsystems approach to process the ERBE data, starting with the input telemetry and ephemeris data from Goddard Space Flight Center (GSFC) and ending with the production of the required science data products.
The first step in this processing procedure is to ingest 24 hours of telemetry data from the ERBS spacecraft into the front-end processing subsystem of the Data Processing System. The data are organized into a format that is common to data from GSFC. Extensive data quality editing and evaluation are performed, including the checking of quality flags appended by the tracking networks and processing systems at GSFC. The operational status of the instruments is determined, and all instrument housekeeping data and selected spacecraft housekeeping measurements are converted to engineering units and edited. Pointing vectors for the optical axes of the detectors are calculated.
At the next processing stage, the raw measurements for each radiometric detector are averaged for each 16 second record and statistical values stored. Sun view and reference view records are then distinguished and converted to irradiances. The conversion algorithms employ calibration coefficients that are based primarily on ground-based calibration data, but which are updated with results from in-flight calibrations as needed. An archival product from the solar monitor measurements is then produced to provide time histories of solar irradiance values. All archival data products are distributed first to the ERBE Science Team for review and validation and then to LaRC ASDC for archival.
There are no plans for reprocessing.
There is a browse product available for each granule in this data set.
The Langley ASDC performs an inspection process on this data received by the data producer via ftp. The ASDC checks to see if the transfer of the data completed and were delivered in their entirety. An inspection software was developed by the ASDC to see if the code was able to read every granule. The code also checks to see if every parameter of data falls within the ranges which are included in the granule. This same code extracts the metadata required for ingesting the data into the IMS. If any discrepancies are found, the data producer is contacted. The discrepancies are corrected before the data are archived at the ASDC.
There are no known limitations or unreliable aspects in the algorithms implemented to generate the ERBE science data.
There are no known problems or inconsistencies in the ERBE data.
None.
Measurements of the total solar irradiance provide one of the important elements of Earth's radiation budget. They also provide possibilities for "climate experiments" by allowing the sensitivity of the radiation budget to various forcings to be studied empirically. One of those forcings is the variation in the Suns total energy output which drives our climate system.
Additional granules will be added to the archive list as data become available.
Sample read software is available for this data set. This code is written in C. A makefile and a readme file are also available to work with the code and data.
The software can be obtained through the Langley ASDC. Please refer to the contact information below. The software can also be obtained at the same time the user is ordering this data set.
Data, programs for reading the data, and user's guides can be obtained through the EOSDIS Langley ASDC on-line system which will allow users to search through the data inventory and place orders on-line.
Langley ASDC User and Data Services Office
NASA Langley Research Center
Mail Stop 157D
Hampton, Virginia 23681-2199
USA
Telephone: (757) 864-8656
FAX: (757) 864-8807
E-mail: larc@eos.nasa.gov
URL: http://eosweb.larc.nasa.gov
The Langley ASDC User and Data Services staff provides technical and operational support for users ordering data.
Select this text for information on the Langley Information Management System which provides an interface to order data from the Langley ASDC.
On a regular basis, individual ERBE data granules are reviewed by local members of the ERBE Science Team. Upon Science Team approval, the ERBE Data Management Team releases the data granule to the LaRC ASDC for archive.
There is a browse image for each granule of data archived at the Langley ASDC.
R. B. Lee III, B. R. Barkstrom, and R. D. Cess, "Characteristics of the Earth Radiation Budget Experiment Solar Monitors," Appl. Optics, 26 (15) 3090-3096, 1987.
R. B. Lee III, M. A. Gibson, N. Shivakumar, R. S. Wilson, H. L. Kyle, and A. T. Mecherikunnel, "Solar Irradiance Measurement: Minimum Through Maximum Solar Activity," Metrologia, Vol. 28, pp. 265-268, 1991.
R. B. Lee III, B. R. Barkstrom, M. R. Luther, R. D. Cess, Solar Irradiance Measurements Using the Earth Radiation Budget Experiment Solar Monitors, Proceedings of the Sixth Conference on Atmospheric Radiation, American Meteorological Society, pp. J5-J8, 1986.
R. B. Lee III, M. A. Gibson, R. S. Wilson, S. Thomas, "Long-term Total Solar Irradiance Variability During Sunspot Cycle 22" Journal of Geophysical Research, Vol. 100, No. A2, pp. 1667-1675, February 1, 1995.
Sorlie, S., February 1993. "Langley DAAC Handbook." NASA Langley Research Center, Hampton, Virginia.
