Dr' Steven A' Lloyd

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Earth-Observing Satellites Remote Sensing
Instruments
Dr. Steven A. Lloyd Chief Scientist NASA GSFC
Earth Sciences DISC Wyle Information Systems,
Inc. the Giovanni Science Team
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Satellite Remote Sensing Instruments

• Fifteen satellite remote sensing instruments are
  accommodated on NASA three flagship EOS
  satellites Aqua, Terra and Aura.

Aqua
Terra
Aura
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Satellite 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

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Satellite Remote Sensing Instruments
Aura Spacecraft

• Terra Spacecraft
• Five Instruments
• ASTER
• CERES
• MISR
• MODIS
• MOPITT

• Four Instruments
• OMI
• TES
• HIRDLS
• MLS

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Remote Sensing of Radiation

• Earth-observing satellite remote sensing
  instruments make observations across the entire
  electromagnetic spectrum.

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Remote 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
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Remote 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)
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Remote 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)
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Remote Sensing of Radiation

• Wavelength resolution or bandwidth is typically
  given as the Full-Width at Half-Max (FWHM),
  assuming a triangular slit-function.

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Remote 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.
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Remote Sensing of Radiation

• Examples of ultraviolet satellite remote sensing
  instruments

Nimbus-7 TOMS
Aura OMI
Earth Probe TOMS
(spectrographs)
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Remote Sensing of Radiation

• Examples of visible satellite remote sensing
  instruments

Aura OMI
SeaWIFS
(spectrographs and filter instruments)
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Remote Sensing of Radiation

• Examples of infrared satellite remote sensing
  instruments

Aura TES
SeaWIFS
Aura HIRDLS
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Remote Sensing of Radiation

• Examples of microwave satellite remote sensing
  instruments

UARS MLS
Aura MLS
CloudSAT
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Remote Sensing of Radiation

• Examples of radio wave satellite remote sensing
  instruments

TRMM PR
QuikScat
CloudSAT CPR
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Remote Sensing of Radiation

• Earth-observing satellite remote sensing
  instruments are either active or passive,
  depending on the original source of the observed
  radiation.

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Active Remote Sensing
Active remote sensing instruments send out a
signal of radiation at a particular wavelength.
Direction of Satellite Motion
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Active 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
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Active 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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Passive Remote Sensing
Passive remote sensing instruments either use the
Sun as the source of radiation
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Passive Remote Sensing
or use radiation emitted by the Earths surface
or atmosphere.
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Passive 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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Passive Remote Sensing
Most satellite remote sensing instruments rely on
passive observations.
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Geostationary 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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Orbital Geometry
Nadir
Solar Zenith Angle
Elevation Angle
Zenith
Horizon
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Low 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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Low 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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Low 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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Instantaneous 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).
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Instantaneous Field-of-View (IFOV)
The nadir (downward-looking) Instantaneous
Field-of-View (IFOV) or footprint represents the
nadir spatial resolution.
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Instantaneous 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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Push-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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Push-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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Cross-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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Cross-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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Global 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.
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Incomplete 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
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Maps 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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Hyperspectral 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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Hyperspectral 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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