|
|
You are here:
Home►Weather Satellites
About Weather Satellites
Weather satellites are used to get a space-bird's eye view of Earth's
atmosphere. There are two main types of weather satellites: polar orbiting and
geostationary. Both monitor the following:
- Day and night cloud images and low-level cloud and fog
images
- Images showing the amounts of water vapor at various
altitudes in the lower atmosphere
- Land temperatures
- Sea surface temperatures
- Winds calculated by measuring cloud motion
- Amounts of solar energy being reflected by various
parts of the Earth
- Infrared, or heat, energy leaving the Earth
- Locations of forest fires
- Estimates of precipitation amounts
- The total amounts of ozone above different locations
The satellites
also relay radio signals from ground-based instruments in remote locations
(GPS), and they also relay signals from downed aircraft and ships or even hikers
in trouble for search and rescue missions.
American satellites (POES and GOES) are named by having a letter
assigned to them before they are launched. Once in orbit, they are given a
number. Polar orbiters (POES NOAA series), geostationary satellites (GOES
series) are given letters before launch, e.g. NOAA-J and GOES-H. Once in orbit
they were renamed NOAA-14 and GOES-7 respectively.
GOES is an acronym for
Geostationary
Operational Environmental Satellite.
"Geostationary"
refers to the 35,800 km high orbit above Earth's equator that keeps these
satellites in geosynchronous orbit.
"Operational" refers to the fact that these satellites are used daily by
scientists all around the world.
"Environmental" refers to the fact that these satellites track clouds,
temperatures, and other weather phenomena, but also Earth-bound solar particles!
"Satellite" refers to the simple fact that these precision instruments
orbit Earth (a planet)!
American weather
satellites (GOES and NOAA) are built and launched by NASA. Once in orbit, NOAA
takes over responsibility of daily operation.
Polar-Orbiting Satellites
These satellites, as the name implies, orbit about Earth's poles in an
almost north-south orbit. Their
orbits are circular, are sun synchronous and orbit about 830 km (morning orbit)
and 870 km (afternoon orbit) above Earth. There are 3 polar-orbiting satellites
in use by NOAA. These polar-orbiting satellites are known as "Advanced
Television Infrared Observation Satellites (TIROS-N or ATN). One crosses the
equator at 7:30am PST, the other at 1:40pm PST. The data they send is acquired
and disseminated by the NOAA Command and Data Acquisition (CDA) stations near
Fairbanks, Alaska and Wallops Island, Virginia. Together, they are able to
provide images that are never more than 6 hours old! Since they complete
1 orbit every 102 minutes, they are able to complete 14 orbits each day and
obtain a complete scan of Earth twice daily.
The names given to the 3 polar-orbiting satellites are:
1. NOAA-14 (formerly NOAA J)
2. NOAA-15
3. NOAA-16
(4.) There is a fourth polar-orbiting satellite, NOAA-12, which still transmits
high-resolution data as a stand-by satellite.
*NOAA-11 (formerly NOAA H) is still in orbit, but as far as I know, it's not
being used and is just expensive space junk.
The primary instrument aboard these satellites is the Advanced
Very High Resolution Radiometer (AVHRR). It is a radiation-detection imager
capable of calculating cloud cover and surface temperature remotely from space.
Surface temperature can be Earth's surface, a cloud's surface, ocean's surface
or any other surface whose temperature is required. The AVHRR on polar-orbiting
satellites scans 6 ranges of wavelengths on 6 different channels:
Channel 1: 0.58 - 0.68 (Daytime cloud and surface mapping)
Channel 2: 0.725 - 1.00 (Land-water boundaries)
Channel 3A: 1.58 - 1.64 (Snow and ice detection)
Channel 3B: 3.55 - 3.93 (Night cloud mapping and sea surface temperature)
Channel 4: 10.30 - 11.30 (Night cloud mapping and sea surface temperature)
Channel 5: 11.50 - 12.50 (Sea surface temperature)
These satellites are also equipped with UV sensors which can
detect ozone levels in the polar atmospheres. During mid-September to
mid-November they detect the "ozone hole" in the stratosphere. More than 16,000
global measurements are transmitted each day via NOAA's CDA stations to NOAA
computers where forecasters use them in their models that news weatherpersons
take credit for!
Geostationary Satellites
Geostationary satellites are used to monitor atmospheric conditions
on a more-or-less continual basis. In actuality, they make complete scans of the
visible globe every 25 minutes and repeat this process every 1/2 hour (MSG
satellites process every 15 minutes). These scans are put together to produce a
time-lapsed film displaying weather conditions from space you've certainly seen
broadcasted by your local news station! These satellites are spin-stabilized and
complete 1 orbit around Earth every 24 hours: the same orbital speed as Earth!
This means they are geostationary, remaining in orbit over the same spot
in sync with Earth. This in-sync orbit is termed, geosynchronous orbit.
They orbit at a height of about 35,800 km above Earth.
There are normally 5 geostationary satellites in operation each
day, with other satellites kept close by and ready for duty if any of the main 5
somehow become defunct. The 5 satellites are:
1. MSG (which replaced Meteosat in 2000) orbits along the Greenwich meridian (no relation to monosodium glutamate!)
2. Insat which orbits near latitude 70ºE
(used for India)
3. GMS which orbits near 140ºE
4. GOES-10 (or GOES-West) which orbits at 135ºW over Earth's equator
5. GOES-8 (or GOES-East) which orbits at 75ºW over Earth's equator It monitors the
Atlantic Ocean where it can spot hurricanes forming off the African Coast.
This shows you what GOES sees at 38,500 km above Earth!
This illustration provided by www.NOAA.gov
The primary instrument aboard these satellites are the Imager
and Sounder. The imager is a radiation-detection imager capable of calculating
cloud cover and surface temperature remotely from space. As with the
polar-orbiters, surface temperature can be Earth's surface, a cloud's surface,
ocean's surface or any other surface whose temperature is required. The imager
on GOES satellites scan 5 ranges of wavelengths on 5 different channels:
Channel 1: 0.6 microns (Visual image)
Channel 2: 0.9 microns (Visual image)
Channel 3: 3.7 microns (Near IR)
Channel 4: 10.8 microns (IR)
Channel 5: 12.0 microns (IR)
The older Meteosat
used 3 channels scanning 3 ranges of wavelengths:
0.4 - 1.1 microns for visual images
5.7 - 7.1 microns for water vapor images
10.5 - 12.5 microns for IR images
However, Europe's newer MSG (not related to monosodium glutamate!) which has replaced Meteosat has at least 8 channels all within the IR range, as well as channels
for ozone and carbon dioxide.
The GOES sounder provides data that scientists use to determine
the vertical temperature and moisture profile of Earth's atmosphere for a given
area. It also is capable of providing surface and cloud top temperatures as well
as ozone distribution. There is also a Search and Rescue transponder, a data
collection and relay system for ground-based data platforms, and a space weather
monitor. The space weather monitor is made up of a magnetometer, and X-ray
sensor, a high energy proton and alpha detector, and an energetic particle
sensor which are all used to monitor the space environment near Earth's
outermost atmosphere. You may have heard the terms, "solar weather", or "space
weather", which are in reference to that which is monitored by GOES space
monitor equipment!
History of U.S. Polar Orbiting Weather Satellites
The first series of polar orbiters was the TIROS series. TIROS is an acronym
for Television Infrared Observation Satellites. This experimental series of
satellites' primary objectives were to show scientists and government agencies
that weather prediction could be enhanced by proper interpretation of data
collected on Earth's atmosphere from space-based satellites. There were 10 TIROS
launched over a 5-year period (1960-1965). The names of the satellites were
TIROS-I, TIROS-II, TIROS-III, TIROS-IV, TIROS-V, TIROS-VI, TIROS-VII, TIROS-VIII,
TIROS-IX, and TIROS-X.
The second series of polar orbiters was the NIMBUS series.
Originally sent up to replace TIROS, scientists ended up using the NIMBUS
satellites to test new remote sensing techniques as well as to sense the
radiative surfaces of Earth's land masses, oceans, and atmosphere. NIMBUS
satellites were also used for new Earth surface mapping techniques, ground data
processing technique as well as sensing vertical profiles of atmospheric
variables. 8 NIMBUS satellites were put into orbit over a 14-year period
(1964-1978). The names of the satellites were NIMBUS-I, NIMBUS-II, NIMBUS-B,
NIMBUS-III, NIMBUS-IV, NIMBUS-V, NIMBUS-VI, and NIMBUS-VII.
The third series of polar orbiters was the ESSA series. ESSA is
an acronym for Environmental Science Services Administration (Satellite). TIROS
set the stage for ESSA series by showing the scientific community that
atmospheric observations from space were invaluable to weather prediction, while
NIMBUS was paving new ways of collecting data. ESSA satellites' primary
objectives were to send back data quantifying Earth's cloud cover and weather
patterns from space. APT Direct Readout ground stations deciminated this data
for forecasts and weather analyses. Just under 400 APT ground stations were set
up worldwide to retrieve ESSA data. There were 9 ESSA satellites launched over a
3-year period (1966-1969). The names of the satellites were ESSA-I, ESSA-II,
ESSA-III, ESSA-IV, ESSA-V, ESSA-VI, ESSA-ESSA-VII, ESSA-VIII, ESSA-IX.
Another series of weather satellites was the ITOS series. ITOS
is an acronym for Improved TIROS Operational System Satellites, also called the
TIROS -M series. There primary objective was to combine the capabilities of ESSA
satellites with information gained from NIMBUS satellites so that all would fall
under one operational program with APT capability. These second generation
weather satellites eventually became known as the NOAA satellites. Satellites in
this series were ITOS-1, NOAA-1, ITOS-B, NOAA-2, ITOS-E, NOAA-3, NOAA-4, NOAA-5.
A third-generation series of polar orbiters went up under what
became known as the TIROS-N program. 4 satellites in all were sent up over a
3-year period. These satellites carried much higher resolution environmental
sensing equipment than previous satellites. The satellites launched were named,
TIROS-N, NOAA-6, NOAA-B, and NOAA-7.
A fourth-generation series of polar orbiters were the ATN
series. ATN is an acronym for Advanced TIROS-N (program). Instrumentation was
more accurate than before, plus the ATN series had more instruments onboard than
any previous satellites. 8 satellites in all went up over a 15-year period
(1983-1998). The satellites launched were named NOAA-8, NOAA-9, NOAA-10,
NOAA-11, NOAA-12, NOAA-13, NOAA-14 and NOAA-15.
History of U.S. Geostationary Satellites
The first series of U.S. geostationary satellites to go into space were the
experimental ATS series. ATS is an acronym for Applications Technology
Satellites. 5 were launched over a 3-year period. The satellites launched were
named, ATS-I, ATS-II, ATS-III, ATS-IV, and ATS-IV. The primary goal was to show
scientists the worth of placing weather satellites in geosynchronous orbit for
purposes of sending back atmospheric data for forecasting. This first-generation
program proved successful, and was the ancestor of the famous GOES program!
The next series to go up was the SMS/GOES series. SMS is an acronym for
Synchronous Meteorological Satellites, and GOES is an acronym for Geostationary
Operational Environmental Satellites. 5 satellites were launched over a 4-year
period (1974-1978) in a joint effort by NASA and NOAA. NASA was completely
responsible for the creation, implementation and operation of the SMS satellites
(SMS-1 and SMS-2), but NOAA operated the GOES satellites (GOES-1, GOES-2 and
GOES-3). These satellites monitored cloud cover 24 hours a day and sent data
back to NASA and NOAA for dissemination.
Following the SMS/GOES series successes, the GOES series continued, this time
with improved weather sensors and the addition of a vertical sounder capable of
providing scientists with a vertical profile of atmospheric variables. 5 of
these advanced series GOES satellites were put into orbit over a 7-year period
(1980-1987). The satellites launched were named, GOES-4, GOES-5, GOES-6, GOES-G,
and GOES-7.
Next came the GOES-Next series. "Next" refers to "Next Generation" of GOES
satellites. Again, improvements were made, including higher resolution images
and the installation of an intermediate IR channel and other scanners. From
1994-1997, 3 satellites were launched: GOES-8, GOES-9, and GOES-10.
Defense Meteorological Satellite Program
The Defense Meteorological Satellite Program (DMSP) is a U.S. military
operation. The following excerpt was taken directly from the NOAA website:
"Although the
DMSP series is not part of the NOAA satellite series, NOAA
receives, processes and archives data collected from three sensors on board
each satellite: Special Sensor Microwave Imager (SSM/I), Special Sensor
Microwave Temperature Sounder (SSM/T), and Special Sensor Microwave
Water Vapor Profiler (SSM/T2). The DMSP is a long term military effort to
monitor meteorological and oceanographic environment of the earth. Current
satellites, F12 and F13, circle the earth in a near-polar, sun-synchronous
orbit,
maintaining an altitude of approximately 850 km. The average scanning swath
width of the SSM/I, SSM/T and SSM/T2 sensors is 1500 km. The National
Climatic Data Center archives the level 1b data from the SSM/I and SSM/T
since August 1987, and the Temperature Data Records (TDR), Sensor Data
Records (SDR), and Environmental Data Records (EDR) since July, 1987.
Sounding products are available from January 1989 forward."
-by Steve W. Woodruff
|
