Satellite Imagery Has Recorded Rainfall

¶ … Satellite Imagery Has Recorded Rainfall in the Amazon

For studying the Earth's atmosphere, satellites have become indispensable even though it has only been 30 years since the first meteorological satellites were launched. Meteorological satellites view the Earth together with their land- and ocean-sensing cousins, on a global perspective which is unmatched and unmatchable by any other observational system. Observing capabilities bring to the earth a new view and a new technology.

Of fundamental importance to space flight and satellite meteorology in particular, was the formation of the National Aeronautics and Space Administration (NASA) on 1 October 1958. NASA has lead the development of all types of scientific satellites used for civilian purposes. (Kidder 2)

There are now newer satellites that have made atmospheric measurements:

Landsat 7 +ETM

Lansat TM4 or

Aster

EO-1

SPOT-5

EROS

IKONOS

Orb View-3

QUICKBIRD (EUMETSAT 2006)

MODIS

These satellites beam images of areas of Earth's surface from Geostationary Satellite Servers. The myriad of satellites that serve the purposes of observation of weather and assisting warning systems continues to be enhanced by technology. New studies show that NASA satellite images can help researchers assess the amount and rapidity of deforestation in the Amazon. (NASA 2006) large fraction of these were developed by NASA. Developing from the first were agencies that now are components of the U.S. National Oceanic and Atmospheric Administration (NOAA), particularly the U.S. Weather Bureau (now the National Weather Service). Operational U.S. meteorological satellites are controlled by NOAA and the U.S. Air Force today.

The first satellite with a meteorological instrument was Vanguard 2, launched 17 February 1959. Developed by the U.S. Army's Evans Signal Laboratory, Vanguard 2 had a pair of photocells behind lenses that, much like today's scanning radiometers, were supposed to sweep out a visible Earth image as the satellite orbited and spun. Unfortunately the satellite wobbled on its axis, causing the scan lines to crisscross, which rendered the data unusable.

Designed by a scientist at the University of Wisconsin named Suomi, the radiometer system was superior. Explorer 6, launched 7 August 1959, was the second satellite with meteorological instruments. It carried an imaging system and a Suomi-radiometer. However, it went into a highly elliptical orbit, and was essentially unusable, although it did return the first Earth photo.

The first successful meteorological instrument on an orbiting satellite was the Suomi radiometer on Explorer 7, launched 13 October 1959. Developed by Verner, Suomi and colleagues at the University of Wisconsin, it consisted of hemispheres, painted either black or white, backed by aluminum mirrors, and mounted on the equator of a spinning satellite. The mirrors reflected the scene back to the hemispheres, such that the hemispheres acted like speres isolated in space. Since the satellite spun, the spheres sampled solar radiation and terrestrial radiation independent of the orientation of the satellite's spin axis. The temperature of each hemisphere was monitored, and its time rate of change was related to the net gain or loss of radiative energy at the sensor. The black hemispheres absorbed all radiation: the white hemisphere reflected solar radiation but absorbed infrared radiation. The difference between the radiation balances of the hemispheres indicated solar radiation. With this data, maps of the solar radiation reflected by the Earth and the infrared radiation emitted by the Earth were made for the first time.

The first satellite completely dedicated to satellite meteorology was launched on 1 April 1960: TIROS (Television and Infrared Observational Satellite). It was the 22nd successfully launched satellite, was hatbox-shaped, about 57 cm in height and 107 cm in diameter and only 120 kg. It used a vidicon camera, which was an adaptation of a standard television camera. A lens focused the image on the light-sensitive face of a cathode ray tube (CRT) and the bright and dark areas resulted in a pattern of electrical charge on the CRT. An electron beam scanned the CRT face to measure the charge. This scanner had 500 lines, each with 500 elements. Scanning the image took 2 s. The voltages measured by the vidicon camera were telemetered to the ground and reassembled into an image.

Nine additional satellites were launched in the TIROS series; the last was launched on 2 July 1965. By then improvements were introduced in the TIROS series. A scanning radiometer, a Medium Resolution Infrared Radiometer (MRIR), was similar to today's imaging instruments. TIROS 3, 4, and 7 also carried improved versions of the Suomi radiometer.

TIROS 8, launched 21 December 1963, introduced Automatic Picture Transmition (APT). A new vidicon camera with 800-line resolution was scanned at the slow rate of 4 lines per second, and the data were immediately broadcast to the Earth at VHF (Very High Frequency) frequencies. The slow transmission rates meant that anyone with inexpensive equipment could directly receive weather satellite images as the satellite passed by twice each day. It is still an important function on today's polar-orbiting weather satellites.

In 1964 a series of experimental meteorological satellites was initiated, the Nimbus series. Nimbus 1, launched 28, 1964 was the first 3-axis stabilized metsat. With the use of momentum wheels controlled by horizon sensors, it rotated once per orbit. The APT camera was therefore much more useful than that of TIROS 8, which only viewed the Earth 25% of the time. Nimbus 1 also was the first sunsynchronous satellite, which means that it passed over any point on Earth at approximately the same time each day.

In the mid-1960s, when metsat coverage become continuous, there have been no undetected tropical cyclones anywhere on Earth. These ocean-born storms used to surprise potential victims. Lives are now saved because of the warnings that metsats make possible.

In total, seven Nimbus satellites were launched. Some experiments on Nimbus 7, launched 24 October 1978, are still operational. The Nimbus series tested many new concepts that have lead to the operational instruments in use today.

In 1966, the U.S. Environmental Science Service Administratino (NOAA's predecessor), commissioned nine satellites, ESSA 1 through 9, which were launched between 3 February 1966 and 26 February 1969. Essentially like the TIROS 9, each flew in cartwheel configuration, but in sunsynchronous orbit, allowing the transmission of Earth's surface almost 100% of the time.

Weather satellites have been known to measure the weather affects on portions of the Earth dependent on high rainfall or low precipitation, such as the Gobi Dessert and the Amazon rain forests. Within a matter of days, NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) can give a regional analysis of land cover, much faster than what Landsat is able to do.

MODIS gives weather personnel multiple images a day and does not require extensive storage and processing in order to evaluate quality data provided by those images, showing areas of clouds, water or high aerosols. Composites are obtained by combining images to show large areas of the Earth.

An article in Satellite Data Applications: Weather and Climate talks about how the satellites may measure the physically-based parameterization of cloud processes and cloud water. The models have started to produce the distributions of a number of cloud water variables on a global scale. The ability to observe this data of various forms of consensate that can be utilized for initialization and validation of model cloud fields is available on a global scale. (Weng 407)

The Special Sensor Microwave Imager (SSM/I) from the U.S. Defense Meteorological Satellite Program (DMSP) is used to measure both raining and non-raining cloud liquid water. Precipitation and ice particles are also measured by the SSM/I scattering index. These measurements are used in a SSMI/Cloud Liquid Water algorithm to find out how the clouds are affected by the thermal emission doe to cloud liquid water droplets and water vapor in the atmosphere. A formula was derived to determine how these clouds affected the Earth. (Earth 2005)

Asner, who has studied satellite observation of the Amazon, says "remote sensing observations have not provided quantitative evidence that climate variation affects Amazon forest phenology or productivity." But he goes on to say that they are able to measure and estimate how much "canopy energy absorption and net primary production of Amazon forests varied interannually." (Asner, 1974, 981)