Title: Dr. Steven A. Lloyd
1Earth-Observing Satellites Remote Sensing
Instruments
Dr. Steven A. Lloyd Chief Scientist NASA GSFC
Earth Sciences DISC Wyle Information Systems,
Inc. the Giovanni Science Team
2Satellite Remote Sensing Instruments
- Fifteen satellite remote sensing instruments are
accommodated on NASA three flagship EOS
satellites Aqua, Terra and Aura.
Aqua
Terra
Aura
3Satellite Remote Sensing Instruments
- Earth-observing satellite remote sensing
instruments are named according to - 1) the satellite or platform and
- 2) the sensor or instrument.
- Aqua Spacecraft
- Six Instruments
- MODIS
- CERES
- AIRS
- AMSU-A
- AMSR-E
- HSB
4Satellite Remote Sensing Instruments
Aura Spacecraft
- Terra Spacecraft
- Five Instruments
- ASTER
- CERES
- MISR
- MODIS
- MOPITT
- Four Instruments
- OMI
- TES
- HIRDLS
- MLS
5Remote Sensing of Radiation
- Earth-observing satellite remote sensing
instruments make observations across the entire
electromagnetic spectrum.
6Remote Sensing of Radiation
- Older Earth-observing satellite remote sensing
instruments typically made observations at only a
few discrete wavelengths or wavelength bands.
Nimbus-7 TOMS
Six wavelength bands (1 nm wide)
312.5 nm 317.5 nm 331.3 nm 339.9
nm 360.0 nm 380.0 nm
7Remote Sensing of Radiation
- Newer Earth-observing satellite remote sensing
instruments typically make observations at many
discrete wavelengths or wavelength bands.
Terra MODIS
36 wavelength bands covering the wavelength range
405 nm (blue) to 14.385 µm (infrared)
8Remote Sensing of Radiation
- Even newer Earth-observing satellite remote
sensing instruments make continuous
multi-spectral observations across a wide
wavelength range using CCD arrays or cameras.
Aura OMI
Two wavelength channels 270-380 nm
(UV) 350-500 nm (Vis) with 0.45-1.0 nm
resolution (FWHM)
9Remote Sensing of Radiation
- Wavelength resolution or bandwidth is typically
given as the Full-Width at Half-Max (FWHM),
assuming a triangular slit-function.
10Remote Sensing of Radiation
- Hyperspectral imaging spectrographs can provide
3-D images or maps of the hyperspectral cube of
contiguous lat?lon?wavelength images using
2-dimensional CCD cameras at hundreds or
thousands of wavelengths.
Hyperspectral cube generated from the NASA
Airborne Visible/Infrared Imaging Spectrometer
(AVIRIS) airborne sensor.
11Remote Sensing of Radiation
- Examples of ultraviolet satellite remote sensing
instruments
Nimbus-7 TOMS
Aura OMI
Earth Probe TOMS
(spectrographs)
12Remote Sensing of Radiation
- Examples of visible satellite remote sensing
instruments
Aura OMI
SeaWIFS
(spectrographs and filter instruments)
13Remote Sensing of Radiation
- Examples of infrared satellite remote sensing
instruments
Aura TES
SeaWIFS
Aura HIRDLS
14Remote Sensing of Radiation
- Examples of microwave satellite remote sensing
instruments
UARS MLS
Aura MLS
CloudSAT
15Remote Sensing of Radiation
- Examples of radio wave satellite remote sensing
instruments
TRMM PR
QuikScat
CloudSAT CPR
16Remote Sensing of Radiation
- Earth-observing satellite remote sensing
instruments are - either active or passive, depending on the
original source of the observed radiation.
17Active Remote Sensing
Active remote sensing instruments send out a
signal of radiation at a particular wavelength.
Direction of Satellite Motion
17
18Active Remote Sensing
Active remote sensing instruments rely upon the
amount or frequency of radiation reflected back
to the satellite instrument by the Earths
surface or atmosphere.
Atmosphere
18
19Active Remote Sensing
An example of an active remote sensing instrument
is the CALIOP (Cloud Aerosol LIdar with
Orthogonal Polarization)
Lidar (laser LIght Detection and Ranging)
instrument on the CALIPSO satellite.
Atmosphere
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20Passive Remote Sensing
Passive remote sensing instruments either use the
Sun as the source of radiation
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21Passive Remote Sensing
or use radiation emitted by the Earths surface
or atmosphere.
21
22Passive Remote Sensing
Passive remote sensing instruments rely upon the
amount or frequency of radiation received by the
satellite instrument from the Earths
surface or atmosphere.
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23Passive Remote Sensing
Most satellite remote sensing instruments rely on
passive observations.
23
24Geostationary Field-of-View (FOV)
sub-orbital point
The field-of-view (FOV) of a Geostationary
satellite (i.e., what it can see from its
vantage point in space) remains the same over
time, and is at most ½ of the Earths surface
(90 longitude one either side of the
sub-orbital point on the equator).
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24
25Orbital Geometry
Nadir
Solar Zenith Angle
Elevation Angle
Zenith
Horizon
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26Low Earth Orbit (LEO) FOV
Satellites in Low Earth Orbit have only a limited
Field-of-View (FOV) compared to Geostationary
satellites, because they are comparatively closer
to the Earths surface.
Therefore, they use a variety of techniques to
expand their coverage of the planets surface.
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27Low Earth Orbit (LEO) FOV
The nadir FOV is defined as directly beneath the
satellite track, when the satellite is overhead
(90 elevation angle from the horizon).
Direction of Satellite Motion
Nadir
90
Horizon
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28Low Earth Orbit (LEO) FOV
The orbit is defined as having a cross-track and
an along-track direction.
Direction of Satellite Motion
Along-Track Direction
Cross-Track Direction
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29Instantaneous Field-of-View (IFOV)
Satellites in Low Earth Orbit have only an
instantaneous Field-of-View (IFOV) what can be
observed in a single pixel or view by the sensor
looking in the nadir-
measured either as a solid viewing angle or as a
geometric shape or footprint on the surface of
the Earth (i.e., 10?14 km2 or 0.25? 0.5
lat/lon).
29
30Instantaneous Field-of-View (IFOV)
The nadir (downward-looking) Instantaneous
Field-of-View (IFOV) or footprint represents the
nadir spatial resolution.
30
31Instantaneous Field-of-View (IFOV)
Note that the off-axis Instantaneous
Field-of-View (IFOV) is larger than the nadir
IFOV,
and thus the spatial resolution is coarser in the
cross-track direction.
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32Push-Broom Sensors
Push Broom sensors provide a line array of
several sensors (e.g., CCD optical arrays, diode
arrays, etc.),
all of which view a small strip of the Earths
surface perpendicular to the motion of the
satellite.
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33Push-Broom Sensors
By stitching together a continuous series of push
broom images, a contiguous swath or ribbon of
data encircling the Earth can be achieved.
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34Cross-Track Scanning Sensors
In Cross-Track Scanning, a scan mirror swings
back and forth along the sub-orbital track,
allowing the sensor to sequentially observed
pixels and trace out a small swath or ribbon of
the Earths surface along the direction of the
satellites motion.
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35Cross-Track Scanning Sensors
Cross-track scanning results in individual
observations (pixels) of varying size, and can
leave gaps between successive orbits if the scan
angle is not wide enough.
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36Spatial Coverage
Nimbus-7 TOMS Orbital Altitude 955 km
EarthProbe TOMS (original) Orbital Altitude 500
km
If the orbit is too low and/or the FOV is too
small, complete global coverage cannot be
obtained with only 16 orbits in a single day.
36
37Incomplete daily global coverages results in
daily global maps composed of ribbons of data
with data gaps between the swaths in the
equatorial regions. Note that for high
inclination satellites, there is still
significant overlap at the poles even when
equatorial coverage is incomplete.
Incomplete Global Coverage
Global View
South Polar View
North Polar View
29 September 1997
38Maps without gaps, which is what most modelers
require as input to their computer simulations,
can be obtained by averaging over 2-3 days (or
more).
Providing Global Coverage
While averaging for multiple days fills in the
orbital gaps and results in complete global
coverage, it results in lower temporal resolution.
28-29 September 1997
29 September 1997
28-30 September 1997
29-30 September 1997
no gaps
smaller gaps
One Day Two Days Three Days
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39Hyperspectral Imaging Sensors
Hyperspectral imaging instruments make
simultaneous observations of 2-D images at a
large number of wavelengths.
Diagram courtesy of Space Computer Corp.
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40Hyperspectral Imaging Sensors
Diagram and caption courtesy of Georgia Tech.
Multiple images in different spectral bands form
an image cube for the same spatial image. Spatial
and spectral analyses are performed on the image
cube to obtain chromatic, textural, and regional
information.
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