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Valid Values: Instruments -
Technology
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Multi-purpose imaging Vis/IR
radiometer
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Instrument designed to address more
objectives by appropriate blending of the characteristics of
spectral
coverage and resolution, spatial resolution, radiometric
accuracy, etc..
Spectral coverage in bands of Vis, NIR, SWIR, MWIR and TIR
(0.4-15 µm).
Number of channels from a few to a few tens, separated by
dichroics and
filters. Channel bandwidths around 10 %. Spatial resolution
typically 30m - 3
km. Applicable in LEO and GEO.
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High
resolution optical imager
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Imaging Vis/IR radiometer whose
characteristics are stressed towards spatial resolution
(typically <30 m).
Spectral coverage in bands of
Vis and NIR (0.4-1.3 µm). Number of channels can be
small (extreme: one,
i.e. panchromatic) or very large (hyperspectral) separated
in-field (array
detectors) or by a spectrometer, or a combination of both.
Channel bandwidths
from 0.5 µm (PAN) to 5 nm (hyperspectral). Applicable only
in LEO.
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Multi-channel/direction/polarization
radiometer
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Imaging Vis/IR radiometer that
addresses parameters observable by exploiting different
viewing conditions
(e.g., to convert radiances into irradiances), different
polarisations (to
reconstruct the electric field, i.e. the Stokes vector) and
more channels (to
collect more spectral signatures). A variety of
configurations are possible.
Multi-polarisation and multi-directionality are appropriate
for short
wavelengths. Channels bandwidths 2-5 %, spatial resolution
typically 0.5-5
km. Applicable only in LEO.
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Medium-resolution
spectro-radiometer
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Used when the number of channels is
high and they are too close to be separated by dichroics and
filters. The
instrument spreads the radiation beam by means of a
spectrometer, but
thereafter only a limited number of channels is selected,
that generally is
re-programmable. Channels bandwidths 1-3 %, spatial
resolution typically
0.5-5 km. Applicable in LEO and GEO.
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High-resolution nadir-scanning SW
spectrometer
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Spectrometers to cover bands in UV,
Vis, NIR and SWIR with spectral resolution typically of
0.1-0.3 %, required
for atmospheric chemistry. Earth viewing so as to measure
vertical profiles
and total columns. Thousands of channels. Spatial resolution
typically 2-20
km. Applicable in LEO and GEO.
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Limb-scanning SW
spectrometer
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Spectrometers to cover bands in UV,
Vis, NIR and SWIR with spectral resolution typically of
0.1-0.3 %, required
for atmospheric chemistry. Designed to provide high vertical
resolution in
the upper troposphere and above by scanning the EarthÕs
limb. Also, scanning
may be performed during occultation of the sun or the moon
or bright
stars.
Thousands of channels.
Spatial resolution typically 1-3 km vertical, 300-500 km
horizontal.
Applicable only in LEO.
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Narrow-band
channel IR radiometer
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Radiometer operating in MWIR and
TIR with many channels of bandwidth around 1 % in absorption
bands of CO2 and
H2O to retrieve temperature and humidity profiles in
cloud-free or partially
cloudy areas. Cross-nadir scanning for vertical profiling. A
few tens of
channels. Spatial resolution typically 10-20 km horizontal,
~ 2 km vertical
(referred to the retrieved profile). Applicable in LEO and
GEO.
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Medium-resolution
IR spectrometer
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Spectrometer operating in MWIR and
TIR with spectral resolution typically around 0.1 % to
retrieve temperature
and humidity profiles from absorption bands of CO2 and H2O
in cloud-free or
partially cloudy areas, and also total columns of some
greenhouse gas species
(and coarse profile of O3). Cross-nadir scanning for
vertical profiling and
total-columns. Many thousands of channels. Spatial
resolution typically 10-20
km horizontal, ~ 1 km vertical (referred to the retrieved
profile).
Applicable in LEO and GEO.
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High-resolution nadir-scanning IR
spectrometer
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Spectrometer operating in MWIR and
TIR with spectral resolution typically around 0.01 %
required for atmospheric
chemistry. Earth viewing so as to measure vertical profiles
and total columns
in cloud-free or partially cloudy areas. Cross-nadir
scanning for vertical
profiling and total-columns. Many thousands of channels.
Spatial resolution
typically 5-10 km horizontal, ~ 1 km vertical (referred to
the retrieved
profiles). Applicable only in LEO.
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Limb-scanning IR
spectrometer
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Spectrometer operating in MWIR and
TIR with spectral resolution typically around 0.01 %
required for atmospheric
chemistry. Designed to provide high vertical resolution in
the upper
troposphere and above by scanning the EarthÕs limb. Many
thousands of
channels. Spatial resolution typically 1-3 km vertical,
300-500 km horizontal.
Applicable only in LEO.
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Multi-purpose
imaging MW radiometer
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Radiometer operating in bands of
frequency ranging from 1 to 300 GHz. A specific instrument
can only cover a
limited part of the range, for instance from 7 to 200 GHz.
Several parameters
can be observed in this range, thus the instrument is
designed by optimally
blending the various features. For certain parameters very
low frequencies
are need (e.g., 1.4 GHz for ocean salinity and soil moisture
in the roots
region). Several channels, of bandwidths often constrained
by frequency
protection regulations. The basic channels operate in
atmospheric windows,
but in few cases absorption channels also are added. Conical
scanning is the
rule, which enables constant incidence angle, thus
homogeneous polarisation
conditions. If full polarisation is implemented, the
instrument provides
sea-surface wind vector. The resolution is
diffraction-limited, thus for a
given antenna (e.g., diameter 180 cm) changes with frequency
(e.g., from 4 to
50 km moving frequency from 90 to 7 GHz). For very low
frequencies, synthetic
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Non-scanning MW
radiometer
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This MW radiometer has the limited
purpose of supporting radar altimeter by providing
information on
total-column water vapour over the sea. The main channel is
centred on the
water vapour band at 23 GHz, with one or two windows around.
The instrument
only points nadir exactly as the radar altimeter, thus
provides measurement
only along track. The resolution is tuned to that one of the
altimeter,
typically around 25 km. Applicable only in LEO.
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Absorption-band MW
radiometer/spectrometer
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Radiometers operating in bands of
absorption from O2 (typical, ~ 54 GHz) and from H2O
(typical: ~ 183 GHz) enable measuring the atmospheric temperature and humidity
profiles in nearly-all-weather conditions. Cross-nadir
scanning is utilised,
though also conical scanners use to include channels in
absorption bands.
Radiometric accuracy is a driver for profiling, thus
scanning speed must be
relatively slow, that implies coarse resolution (typical, 50
km for 54 GHZ,
15 km for 183 GHz, horizontal; the vertical, referring to
the product, is ~ 2
km). Applicable in LEO; however by adding higher frequencies
(e.g. 118 and
425 GHz for O2 and 380 GHz for H2O) sounding is also
possible from GEO.
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Limb-scanning MW
spectrometer
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Spectrometer operating in the
millimetre-submillimetre range (30-3000 GHz) with spectral
resolution
typically around 0.01 % required for atmospheric chemistry.
Designed to
provide high vertical resolution in the upper troposphere
and above by
scanning the EarthÕs limb. Some thousands of channels.
Spatial resolution
typically 1-3 km vertical, 300-500 km horizontal. Applicable
only in LEO.
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Imaging radar
(SAR)
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If radar is used, the problem of
diffraction-limited resolution in MW still applies. In this
case, however, by
analysing range, azimuth and Doppler effect of the
(coherent) signals,
synthetic aperture can be implemented, and resolutions
typically of 10-30 m
can be achieved. Several combinations of polarisations in
transmission and reception
can be implemented. Resolution can be traded-off with swath
(e.g. 30 m / 100
km or 150 m / 400 km). Interferometry between views from
different passes
enable appreciating changes. SAR exploiting different bands
(L, S, C, X)
emphasise different features. Applicable only in LEO.
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Lightning
imager
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Detector matrix all-time watching
the earth in a very-narrow O2 band at 777.4 nm, to count the
flash rate and
intensity in the instantaneous field of view (5-10 km).
Applicable in LEO
and, better, in GEO.
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Cloud
and precipitation radar
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Nadir-pointing radar to observe the
profile of liquid and ice water in clouds. Depending on the
frequency, the
radar better observes liquid precipitation (~ 14 GHz), solid
precipitation (~
35 GHz) or non-precipitating clouds (~ 94 GHz). The antenna
size is
dimensioned for a ground resolution typically of ~ 5 km and
the vertical
resolution is 250-500 m. Pushbroom multi-feed provides
limited swath (few
100Õs km for lower frequencies, basically zero at the
highest frequency). Applicable
only in LEO.
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Radar
scatterometer
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Radar with very accurate
calibration, to observe an earthÕs spot from several
directions (ahead,
after, aside) and measure differential backscatter
coefficients (s0) from sea
capillary waves (thus observing surface wind). On land, the
s0 are correlated
with soil moisture. Two concepts exist: electronic scanning,
side looking,
exploiting C-band (~ 5 GHz); and conical scanning,
exploiting Ku-band (~ 13
GHz). The resolution is typically 25-50 km, the swath
1100-1500 km.
Applicable only in LEO.
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Radar
altimeter
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Nadir-viewing radar for very
accurate ranging measurement between satellite and surface.
The spread of
echoes provides information on significant wave height, the
intensity on the
wind speed, the multi-temporal analysis the ocean dynamic
topography and the
geoid. The instantaneous field of view is ~ 25 km and moves
along track. The
radar altimeter operates in Ku-band (~ 13 GHz) with the
support of C-band (~
5 GHz) for correction from ionospheric rotation; and is
associated to a
nadir-pointing MW radiometer for water vapour correction.
Applicable only in
LEO.
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GNSS
receiver
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Precision positioning system
exploiting the differential phase of signals from a few
satellites of the
Global Navigation Satellite System. Applicable only in LEO.
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GNSS
radio-occultation receiver
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GNSS receiver equipped with
directional antennas to receive the signal from one of the
GNSS satellites
during occultation, and measure the phase, thus the bending
angle and the
refractivity index profile. Simultaneously, a companion GNSS
receiver
provides precision positioning. The refractivity index is
associated to
temperature, humidity and density. The vertical resolution
of the product can
be as good as 0.5 m, the horizontal resolution is
conditioned by the limb
geometry (~ 300 km). Applicable only in LEO.
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Atmospheric
lidar
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Lidar measuring the backscattering
of atmospheric components such as clouds and aerosol. One or
two wavelengths
can be exploited, in UV or Vis or NIR. Nadir-only,
resolution typically ~ 100
m both horizontal and vertical. Applicable only in LEO.
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Doppler
lidar
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Lidar measuring the Doppler shift
of echoes from atmospheric components such as air molecules
and aerosol. A UV
wavelength is exploited, but other ones are possible. Side
looking, measuring
the radial component of wind in clear air. The resolution is
controlled by
sampling needs, and may be in the range of 100-200 km, aside
of the orbital
track. Applicable only in LEO.
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Lidar
altimeter
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Altimeter that exploits lidar in
order to detect polar ice edge with an accuracy of ~100 m
instead of the 25
km of the radar altimetry. Designed to measure polar ice
thickness and
ultimately topography. Other observations common to
atmospheric lidar also
possible, such as vegetation canopy height. Applicable only
in LEO.
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Broad-band
radiometer
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Radiometer with channels that
integrate the total radiation emerging from TOA (0.2-100 µm)
and the fraction
of reflected solar radiation (0.2-4.0 µm). Ancillary
channels in atmospheric
windows may be present. Capability of observing under more
viewing directions
so as to help converting radiances into irradiances may be
present.
Resolution in the range of 20-50 km. Applicable in LEO and
GEO.
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Solar
irradiance monitor
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Observes radiation coming from the
Sun, either integrated (i.e., in the interval 0.2-10 µm,
observed by cavity
radiometers) or spectrally resolved (e.g., in the interval
0.2-2 µm, observed
by a spectrometer), or for special features (X-rays, UV,
etc,). Applicable in
LEO and GEO.
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Gradiometer/accelerometer
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System designed to be sensitive to
anomalies of the EarthÕs gravity field. Implemented in
several modes by
approprate networking of accelerometers, tensors, etc.).
Applicable only in
LEO.
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Satellite-to-satellite ranging
system
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System to accurately measure the
distance (e.g. by K-band, ~ 25 GHz) and its variations
between satellites in
coordinated orbits. Used to measured long-wave anomalies of
the EarthÕs
gravity filed. Applicable only in LEO.
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Magnetometer
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System designed to measure the
EarthÕs magnetic field in its various components (scalar,
vector). Applicable
only in LEO.
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Electric field
sensor
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System designed to measure the
EarthÕs electric field. Applicable only in LEO.
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Space
environment monitor
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Package of instruments mainly to
measure the energy of charged particles hitting the
platform, both integrated
and spectrally analysed. A main purpose is to monitor the
platform safety.
Applicable in LEO and GEO.
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Laser
retroreflector
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Mirrors (generally cube corners) to
reflect laser beams sent to the satellite by ground
laser-equipped sites
during positioning sessions. Applicable only in LEO.
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Radio-positioning
system
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System of transponders involving
satellite and ground transmitting-receiving stations.
Applicable only in LEO.
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Star
tracker
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CCD imager that tracks bright
stars, recognise the pattern and sends information to the
satellite attitude
control system. Applicable in LEO and GEO.
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Data
collection system
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Transponder that relays to ground
the data collected in situ by Data Collection Platforms. It
might localise
the DCP if mobile (only from LEO). It might retrieve the
collected data after
interrogation of the DPC. Applicable in LEO and GEO.
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Communications
system
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To command and control the
satellite, to transmit the data from the satellite to the
ground, to
transpond data from ground sites to other ground sites via
satellite, etc..
It includes Search & Rescue by satellite. Applicable in
LEO and GEO.
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