TIROS and Nimbus - Remote Sensing Application - facegis.com
TIROS and Nimbus

The first experimental meteorology series began with TIROS-1, launched on April 1, 1960. TIROS stands for Television Infrared Observational Satellite. The main instrument was a vidicon, which is a modified television camera that scanned through 500 lines, each containing 500 pixels. Although desinged to function primarily to learn what that kind of satellite can contribute to meteorology, TIROS (and Nimbus) both provided useful insights as well into land observations for earth resources applications.

Because of its fame as a first, this satellite (a second copy) has been enshrined at the National Air and Space Museum in Washington, DC:

A copy of TIROS-1; it is 42 inches wide.

We show here one of the nearly 23,000 images returned from TIROS-1:

TIROS-1 image.

TIROS images are mosaicked to provide global panoramas of cloud cover:

Worldwide cloud distribution as imaged by TIROS.

TIROS-2 included the Medium Resolution Infrared Radiometer (MRIR). The TIROS-8 vidicon had an 800-line resolution and was the first to use the Automatic Picture Transmission (APT) technique. The TIROS series (10 in all) was non-polar following orbital inclinations between 48° and 58° . The first eight TIROS maintained orientation by spinning at 12 revolutions/minute, which limited the time during which the camera pointed at Earth. TIROS-9 followed a "cartwheel" spin pattern (spin axis perpendicular to the orbital plane), which facilitated coverage to allow strips of images that users could mosaick to provide global composites:

TIROS-9 mosaic global composite image.

TIROS-N, the last in the series, was much different from TIROS-1, as seen here:


The next fleet of Metsats, the Nimbus series (total of seven), flown from 1964 to 1978, was dedicated largely to research and development experiments. We name the instruments used in this series in this table:

Nimbus-series instrument chart.

Nimbus-1, launched on August 28, 1964, was the first to be put in a sun-synchronous orbit (now the norm for polar satellites). It used a three-axis stabilization technique (based on flywheels) that kept it pointed constantly at Earth. Nimbus 1, shown below, looks remarkably like ERTS-1 (Landsat). It should - Landsat used the same spacecraft but of course had different sensors.

The Nimbus spacecraft.
Payload on Nimbus-1.

Nimbus carried several instruments including the Advanced Vidicon Camera System (AVCS, an APT) and the High Resolution Infrared Radiometer (HRIR), which operated in the 3.6-4.2 µm interval. An example of a Nimbus 1 HRIR image, taken at night over western Europe, appears next, on the top (note the distortion that enlarges Germany and Sweden relative to southern countries - the Italians may be aggrieved by the shrinking of their "boot"!). On the bottom is a visible Image Dissector Camera System (IDCS) image of the southeast U.S., as seen by Nimbus 3:

Nimbus-1 HRIR image taken at night over western Europe.
Nimbus-3 IDCS image of the southeast U.S.

To compare the information obtained in the visible (left) and the thermal infrared (right), look at this image pair of the Gulf of Mexico acquired simultaneously by Nimbus 4.

Nimbus-4 images (visible and thermal infrared) of the Gulf of Mexico, November 2 1978.

In the next image we get a feel for what one can see at a resolution of 1.1 km (0.7 mi), attained by the IDCS visible channel on Nimbus 3. Under optimal viewing conditions (no clouds), parts of southwestern Wyoming and a bit of Utah appear here.

A Nimbus 3 vidicon image of southwestern Wyoming and northern Utah (date unknown).

The basins generally are highly reflective, and the mountains tend to stand apart because of dark tones associated with evergreen vegetation. Compare this image with this next Landsat 1 MSS mosaic of the entire State of Wyoming that was made by General Electric for me (NMS) as part of my Wyoming project in which I was Co-Investigator with the Geology Department at the University of Wyoming:

Wyoming and parts of surrounding states; a Landsat-1 mosaic.

14-10: The above Nimbus image was the first remote sensing product ever worked on by the writer (NMS) when I transferred in 1970 from the planetary to the remote sensing programs at NASA Goddard Space Flight Center. Just for fun, why don't you fit the Nimbus image into the Landsat mosaic - and check the answer. ANSWER

Nimbus 3 (launched April 14, 1969) also was the first to use atmospheric sounders extensively, along with its Infrared Interferometer Spectrometer (IRIS ), operating between 6 µm, and its 25 µm and Satellite Infrared Spectrometer (SIRS), sensing in the 15 µm region. Nimbus 4 (April 8, 1970) carried the Backscatter Ultraviolet (BUV ) radiometer, becoming the first Metsat to measure atmospheric ozone.

Two instruments on Nimbus 5 (December 11, 1972) are of special significance. The Surface Composition Mapping Radiometer (SCMR) uses two thermal bands, 8.4-9.5 µm and 10.2-11.4 µm, to produce color-coded temperature maps, such as this image of Florida and Cuba and surrounding waters, made from the 8.8 µm channel:

Colored Nimbus-5 SCMR image of Florida and Cuba.

Ratios of radiant temperatures measured by the two bands provide a qualitative estimate of SiO2 content of rocks and soils. This process uses the concept of "restrahlen", a German term that refers to decreased emissivity because of resonance vibrations associated with silicon-oxygen bonds in silica tetrahedra. As the silica content increases, the emissivity decreases more and also shifts as wavelengths become longer.

The Electronically Scanning Microwave Radiometer (ESMR ) on Nimbus 5 operated at a 19.35 GHz frequency (1.55 cm wavelength) to sense brightness temperatures of the surface and atmosphere. This instrument was capable of sensing surface ice temperatures, especially in the polar regions, as shown in this time series of maps that plot the percentage of ice cover around Antarctica on a monthly basis in 1974. The ESMR was also the first to use microwave absorption to estimate precipitation (rain rates) by quantifying increases in optical depth, which correlate to higher brightness temperatures. The ESMR on Nimbus 6 (June 12, 1975) was set at 37 GHz (0.81 cm).

Time series of maps plotting the percentage of ice cover around Antarctica on a monthly basis in 1974, taken by the ESMR on Nimbus-5.

Nimbus 7 carried eight highly complex sensors which were all improved versions of sensors previously flown on Nimbus satellites. They were a Limb Radiance Inversion Radiometer, a High Resolution Infrared Radiation Sounder, an Earth Radiation Budget experiment, a Scanning Multichannel Microwave Radiometer (SMMR), a Pressure Modulated Radiometer, a Solar Backscatter UV/Total Ozone Mapping Spectrophotometer, a Temperature, Humidity Infrared Radiometer and a Tropical Wind, Energy Conversion and Reference Level experiment.

The Scanning Multichannel Microwave Radiometer (SMMR), flown on Nimbus 7 (launched October 24, 1978), and again on Seasat, consists of a 5-channel (0.81, 1.36, 1.66, 2.80, 4.54 cm), dual-polarization instrument that provides data of value to many applications: ocean circulation, low altitude winds, water vapor, cloud liquid water content, sea ice type, extent, and concentration, snow cover, moisture distribution, and rainfall rates. Data on tropical rainfall for the months of 1986 over the Indian Ocean and South Asia is one such product:

Monthly mean rain rates over the Indian Ocean and South Asia for 1984, taken by the SMMR on Nimbus-7.

The SMMR monitored ice in the Antarctic shelf during 1985, as displayed for four months here:

Four maps at different seasons in 1985, showing ice buildup (in reds, yellows, and browns) around the Antarctic perimeter; image data from SMMR on Nimbus 7.

The first Total Ozone Mapping Spectrometer (TOMS) on Nimbus 7, which is still operating, measures UV reflectivities at 0.312, 0.317, 0.331, 0.340, and 0.380 µm. It calculates ozone quantities from the ratio of the returns in the 0.312/0.331 µm wavelengths. As an example of a global ozone map, here is the plot of data obtained on May 14,1992.

Total global ozone map taken by Nimbus-7/TOMS on May 14, 1992.

(Note: A Dobson unit is the response at 4 wavelengths by a Dobson spectrometer from which the total ozone from ground to the outer atmosphere can be measured and then recalculated as a compressed column of ozone equivalent to a 0.01 mm thick, measured over a fixed area centered on Labrador in eastern Canada and adjusted to a STP of 1 atmosphere and O° C.)

In the above maps, the ozone content is higher in high latitudes in springtime. The lower values closer to the equator are of concern because high ozone content affords greater protection from harmful UV radiation.

The South Polar ozone hole has grown wider since 1992. Here is a TOMS image of much of the southern hemsphere, centered on Antarctica, which in September, 2000 disclosed the largest expanse of high ozone levels yet recorded; the hole since has shrunk a bit.

TOMS map of the distribution of Ozone in the Southern Hemisphere in September, 2000.

We can also use the TOMS to monitor SO2 in the atmosphere. After some major volcanic eruptions, it tracked extensive clouds of SO2-enriched ash and gases injected into the upper atmosphere daily across much of the world, until they dissipated below detection levels. Here is the status on June 20, 1991 of the cloud produced by the Mt. Pinatubo eruption in the Philippines.

Colored Nimbus-7/TOMS image monitoring the sulfur-dioxide in the atmosphere during the Mt. Pinatubo eruption on June 20, 1991.

TOMS has proved very useful in monitoring other kinds of atmospheric disturbances such as massive smog buildups that persist over time. Forest fires in Indonesia and elsewhere from September through November of 1999 led to a huge elongate trail of gases that were carried by winds westward to Africa. This TOMS image should the smog and associated clouds near its maximum extent:

Smog and clouds that built up from widespread burning of forests and grasses in Indonesia and neighboring countries in 1997; a TOMS image.

The first Solar Backscatter UltraViolet (SBUV) sensor was on Nimbus 7 (also SBUV/2 on NOAA-9, -11, and -14), sharing some of the components of the TOMS. The SBUV had 12 channels in the UV region providing coverage between 160 and 400 nm. Shown below is a SBUV/2 map of ozone distribution (in Dobson Units) for the South Polar (Austral) Spring. Then, beneath that are graphical data sets for areas of coverage in that region for the months of September through December of the years 2000 and 1999, and three curves summarizing grouped data for 1990-99:

SBUV/2 map of ozone in the polar regions of the Southern Hemisphere
Areal extent of the austral ozone hole for the months and years indicated; SBUV data.

Both the TIROS and Nimbus programs were initiated by NASA. Later ones in the two series included NOAA as a major participant and eventual operator. There are other U.S. and foreign Metsat series: For a nearly complete listing of polar orbiting meteorological satellites (the POES group), consult this Colorado State website.

Source: http://rst.gsfc.nasa.gov