HISTORY of TOVS and TIROS-N series
- “TOVS” is an abbreviation used to identify a suite of three instruments that flew on board series of NOAA satellites, commencing with TIROS-N, in October, 1978. The series continued with NOAA-6,7… , and ended with NOAA-14 launched in April 1995 and decommissioned in May, 2007. Sometimes this series is referred to as “TIROS-N” series. The time coverage of each of the TIROS-N series satellites can be found here.
TIROS stands for “Television InfraRed Observation Satellite”, whereas TOVS is the TIROS Operational Vertical Sounder. (See Acronyms)
It is essential to think of TOVS as a suite of three instruments: HIRS/2, MSU, and SSU. Thus, TOVS can be considered as the predecessor of the AIRS mission flown on the NASA’s Aqua satellite.
SSU instrument was not flown on NOAA-10 and NOAA-12.
The TIROS-N Guide from NOAA is an excellent source of information on TOVS and other instrumentation flown on the TIROS-N series.
The Advanced TIROS Operational Vertical Sounder (ATOVS) system was deployed when NOAA-15 (K) was launched in the Spring of 1998, replacing the aging TOVS suite of instruments.
As the predecessor to AIRS, TOVS was the first suite of spaceborne instruments to provide measurements (infrared and microwave radiances) from which to retrieve global profiles of temperature and moisture, cloudiness, and outgoing longwave radiation (OLR).
Fundamental meteorological parameters such as atmospheric temperature, humidity, cloud properties and surface properties can be continuously measured by earth-orbiting satellites. By placing a satellite in a polar sun synchronous orbit, most of the entire planet can be sampled on a daily basis, excluding areas of orbital gores. However, with averaging of the data over five days and over a month almost complete coverage on a 1 degree latitude by 1 degree longitude is available. This data provides a means to investigate long-term climate change and interannual variability of important meteorological quantities. It is also useful for studying local and/or periodic phenomena such as precipitation patterns, sea surface temperature anomalies (e.g., El Nino) and stratospheric warmings, to name a few.
TOVS was included in the joint (NASA–NOAA) Pathfinder program designed to produce quality satellite-derived climate datasets through analysis of NOAA operational satellite data by community consensus algorithms. In the case of TOVS, many types of algorithms existed, each with potential benefits and limitations. Consequently, it was decided to analyze TOVS data using a number of different methodologies, or paths. Three basic methodologies were identified and included in the TOVS Pathfinder dataset.
A physically based interactive retrieval methodology, called Path A or model dependent, produced full retrievals of temperature–moisture profiles as well as fields of other geophysical parameters derived from the data (Susskind, 1997). Aside from providing accurate first guess information, use of the interactive system also facilitated the ability to remove systematic errors between observed and computed radiances and improved the capability to handle effects of clouds on the radiances.
The second type of methodology, called Path B (model independent) retrievals, is also a physically based full retrieval system but uses a pattern recognition first guess (Chedin et al. 1985). This is an algorithm developed by Atmospheric Radiation Analysis group (ARA) at Laboratoire de Mtorologie Dynamique of the CNRS (France).
The last type of methodology, referred to as Path C, did not produce detailed retrievals but generated only coarse layer temperature climate indicators based on linear combinations of observed radiances in MSU channels (Goldberg and Fleming, 1995).
As of 2011, only the data from Path A and B are available from the GES DISC, in HDF4 format, under a limited support as legacy data.
Samples of retrievals are shown in the figures below. The data are a collection of daily, five day averages and monthly averages with coverage during the years 1985 - 1988 from the satellites NOAA-9 and NOAA-10.Data for 1989 from NOAA-10 and NOAA-11 was added by June of 1996.
- What do these data look like?
- What can I do with these data?
- What are the dataset parameters, temporal and spatial resolution and coverages?
- What makes this dataset unique?
- What kind of hardware and software do I need?
- How can I get these data?
The monthly average temperature and water vapor amount for layers of the atmosphere are two of the eleven parameters of the data that can be used to study climate and climate changes.
1.1 Monthly Temperature Averages
AVERAGE 1985 MONTHLY TEMPERATURES IN THE LAYER FROM SURFACE TO 500 MB, DERIVED FROM TOVS MEASUREMENTS TAKEN ABOARD THE NOAA-9 SPACECRAFT. In addition monthly average temperatures for the atmosphere between 500 to 300 mb, 300 to100 mb, and 100 to 30 mb are available.
1.2 Monthly Water Vapor Averages
AVERAGE 1985 MONTHLY PRECIPITABLE WATER ABOVE THE SURFACE, DERIVED FROM TOVS MEASUREMENTS TAKEN ABOARD THE NOAA-9 SPACECRAFT. The precipitable water represents the vertically integrated water vapor from a particular pressure level (in this case, the surface) to the top of the atmosphere. In addition monthly averages of the precipitable water above 850 mb, 700 mb, 500 mb, 300 mb are also available.
2.1 Measure Climatic Change
With a sufficiently long data record, climatic change may be discernible by averaging quantities such as temperature, moisture, and outgoing longwave radiation (OLR) over weekly or monthly periods and then using statistical techniques to isolate any possible trends in the data.
5-day means for temperature, surface skin temperature, precipitable water, and outgoing longwave radiation
2.2 ObserveEl Niño Phenomena
"El Niño" (Spanish for the Christ child) is the most important climate phenomenon known on a multi-year time scale. The name El Niño has been used by Peruvian fishermen for a long time to identify a phenomenon of warming of the ocean surface waters, often occurring at the end of the year and lasting for several months. Nine events have been recorded in the past forty years. The occurrence of El Nino can be correlated with changes in precipitation patterns throughout the tropical Pacific ocean including Australia, South America and even portions of North America. The "El Niño" event for1986-1987 can be seen in the TOVSdata by taking the difference in the sea surface temperaturefor the months of April in 1987 and 1988.
Full Data Set: Parameters, Temporal and Spatial Resolution and Coverage
A set for seventeen parameter groups containing basic statistics such as the mean, standard deviation, and number of samples for each parameter within every 1 degree grid box is also available. The atmospheric temperature is reported at more pressure levels than in the case of the subsetted dataset described above. In addition, the data is packaged in HDF (Hierarchical Data Format), resulting in files that are self-documenting and readable on a variety of diverse computer architectures.Each HDF file is about 30 MBytes in size and contains the data for all parameters as well as metadata and annotations describing the data and its characteristics.These data are also available as global 5-day or monthly averages, but unlike the smaller data set above, separate files have been created for the daytime and nighttime portions of the orbits. The subsetted data was derived from the full HDF data set.
|TEMP||TEMP_STD||TEMP_COUNT||360x180x12||Vertical temperature profile at 12 levels|
|CLTEMP||CLTEMP_STD||CLTEMP_COUNT||360x180x4||Mean temperatures for 4 coarse layers|
|PRWAT||PRWAT_STD||PRWAT_COUNT||360x180x5||Total precipitable water above 5 levels|
|TSURF||TSURF_STD||TSURF_COUNT||360x180||Surface skin temperature|
|FCLD||FCLD_STD||FCLD_COUNT||360x180||Effecitve total cloud fraction|
|FCLDP||FCLDP_STD||FCLDP_COUNT||360x180x7||Effective cloud fraction, 7 ISSCP layers|
|PCLD||PCLD_STD||PCLD_COUNT||360x180||Effective cloud top pressure|
|TCLD||TCLD_STD||TCLD_COUNT||360x180||Effective cloud top temperature|
|ZANGLE||ZANGLE_STD||ZANGLE_COUNT||360x180||Effective satellite zenith angle|
|TIME||TIME_STD||TIME_COUNT||360x180||Time of day|
|TOZ||TOZ_STD||TOZ_COUNT||360x180||Total ozone index|
|OLR||OLR_STD||OLR_COUNT||360x180||Outgoing longwave radiation|
|LCRF||LCRF_STD||LCRF_COUNT||360x180||Longwave cloud radiative forcing|
|SPHUM||SPHUM_STD||SPHUM_COUNT||360x180x5||Specific humidity profile at 5 levels|
|PSURF||PSURF_STD||PSURF_COUNT||360x180||Model forecast surface pressure|
It provides full global coverage of surface thermal properties and the vertical distribution of temperature and moisture in the atmosphere on a daily basis. Thus it provides important information pertaining to the entire three dimensional structure of the atmosphere and its evolution with time.
Because this dataset has been generated with a single, fixed algorithm, and because considerable care has been taken to remove systematic biases, the data may potentially be used to detect long term climate change once a sufficiently long record of historical TOVS measurements has been processed.
The data set comes principally from satellite measurements but the results are also constrained to be dynamically consistent with a global circulation model (GCM), which provides an optimal measure of the state of the atmosphere for each 6-hour synoptic period.The system also uses in-situ measurements from radiosondes, ships and buoys to remove systematic biases in both the measured radiances and the derived temperature and moisture profiles (see Susskind et al., 1984).
The Path A and B data currently supported by GES DISC are in HDF4 format, and are "externally" compressed. They need to first be "unzipped", before attempting to read the files with any HDF-compatible software package or tool. The utility "gzip" can do the unzipping. To open and read the uncompressed HDF file, various packages and tools can be used: IDL, MatLab, Fortran, HDFview, etc. (NASA does not endorse one commercial package over another.)
Command-line utilities from the HDF Group, like ncdump and hdp, can be used to quickly see the file content, and even dump out data in binary or ASCII (text) format. The hdp with the "dumpvd" option, makes it extremely easy to see TOVS data file annotation. E.g.:
>hdp dumpvd TOVS_5DAYS_AM_B940131.E940204_ND.HDF
will print on the monitor a detailed annotation for the dataset.
The HDF Group also provides a simple tool with java-based user interface, HDFView. This tool is very convenient to explore HDF files content, and produce simple graphic and image previews.
Simple Fortran routines, legacy from earlier years of TOVS support, can be found in this TAR archive. They, however, need to be compiled. Compiling guidance is provided in the README packaged with the fortran code in the TAR.
There are two basic ways to get TOVS Path-A and -B data from GES DISC: i) Anonymous FTP, and ii) Interactive search using Mirador.
- Anonymous FTP: ftp://disc1.gsfc.nasa.gov/data/s4pa/tovs
The directory tree on the FTP server have the patterns:
TOVSA [D,5,M] [NT,NF,NG,NH,ND] Or
TOVSB [D,5,M] [NG,ND]
Where:[NT,NF,NG,NH,ND] - which satellite, correspondingly: TIROS-N, NOAA-F,G,H,D
A,B - Path-A,B
[D,5,M] - stands for Daily, 5-day (pentad), and Monthly
Interactive, Mirador: http://mirador.gsfc.nasa.gov
Chedin, A., Scott, N. A., Wahiche, C., and Moulinier, P. 1985 The Improved Initialization Inversion Method: A High resolution Physical Method fo Temperature Retrievals from Satellites of the TIROS-N Series.J. Climate Apd. Met. 24:128:143.
Goldberg, M., and H. Fleming, 1995: An algorithm to generate deep layer temperatures from microwave satellite observations
for the purpose of monitoring climate change. J. Climate, 8, 993–1004.
Kidwell, K. 1991. NOAA Polar Orbiter Data User's Guide. NCDC/SDSD. National Climatic Data Center, Washington, DC.
Susskind, J., J. Rosenfield, D. Reuter, and M.T. Chahine. 1984. Remote sensing of weather and climate parameters from HIRS2/MSU on TIROS-N. J. Geophys. Res., 89:4677-4697.
Susskind, J., P. Piraino, L. Rokke, L. Iredell, A. Mehta, 1997: Characteristics of the TOVS Pathfinder Path A Dataset. Bull. Amer. Meteor. Soc., 78, 1449–1472.
AIRS: Atmospheric InfraRed Sounder
Ascending Orbit (AM Orbit): A polar orbit traversing from the south pole to the north pole.For the NOAA sun synchronous polar orbital satellites this orbit crosses the equator during daylight hours.
Descending Orbit (PM Orbit): A polar orbit traversing from the north pole to the south pole.For the NOAA sun synchronous polar orbital satellites this orbit crosses the equator during nightime hours.
DAAC: Distributed Active Archive Center, a repository for earth science data.
El Niño(Spanish for the Christ child) This is the most important climate phenomenon known on a multi-year time scale. The name El Nio has been used by Peruvian fishermen for a long time to identify a phenomenon of warming of the ocean surface waters, often occurring at the end of the year and lasting for several months and which induces significant climactic change over the entire world.
FTP: File Transport Protocol, a means of moving files over the Internet.
GCM: Global Circulation Model, a time evolving simulation of the atmosphere using hydrodynamic equations that incorporates satellite measurements of the atmosphere with in-situ measurements to constrain the model.It can be used to interpolate between satellite and in-situ measurements or to predict future states of the atmosphere on a time scale of hours up to a few days.
HIRS/2: High Resolution Infrared Radiation Sounder 2. The HIRS/2 instrument measures radiation emitted by the Earth- atmosphere system in 19 regions of the infrared spectrum between 3.7 and 15 microns. A visible channel is also available to measure the albedo of Earth's surface.
MSU:The Microwave Sounding Unitinstrument is a four channel Dicke radiometer making passive microwave radiation measurements in four regions of the 50 GHz oxygen emission spectrum.
NOAA: National Oceanic and Atmospheric Administration
In-situ Measurements: Measurements of a phenomena at the spatial location where the phenomena is occurring such as by a radiosonde or a ship as opposed to remotely sensed data as by a satellite.
OLR: Outgoing Longwave Radiation, energy radiated away from the atmosphere to space, integated over all frequencies in the earth's infrared spectrum (generally 2 to 20 microns)
Polar Orbit: An orbit passing nearly over the poles.
Radiosonde: A device carried by a weather balloon that measures atmospheric pressure, temperature, and moisture and transmits the measurements by radio to a ground station.There is a world wide network of radiosondes providing atmospheric measurementsup to 4 times daily.
Spatial Resolution: the size of the smallest object recognizable using the detector.
Sun Synchronous: An orbit that passes over the equator at the same local time each day.
SSU: Stratospheric Sounding Unit, a three channel pressure modulated radiometer for sensing radiances emitted from the stratospheric part of the atmosphere.
TIROS: Television InfraRed Observation Satellite
TOVS: TIROS Operational Vertical Sounder, a suit of three instruments that measures upwelling radiation from the atmosphere from which surface properties, clouds, and the vertical structure of the atmosphere can be determined.