Microwave Remote Sensing: Principles and
Applications
• Outline
– Introduction to RSL at the University of Kansas
– Introduction and History of Microwave Remote Sensing
– Active Microwave Sensors
• Radar Altimeter.
• Scatterometer.
• Imaging Radar.
– Applications of Active Sensors
• Sea ice.
• Glacial ice
• Ocean winds.
• Soil Moisture.
• Snow.
• Vegetation.
• Precipitation.
• Solid Earth.
11/18/02 University of Kansas
Microwave Remote Sensing: Principles and
Applications
• Passive Microwave Sensors
– Radiometers
• Traditional
• Interferometer
• Polarimetric Radiometer
• Application of Passive Microwave Sensors
• Sea ice.
• Glacial ice
• Soil Moisture.
• Atmospheric sounding
• Snow.
• Vegetation.
• Precipitation
11/18/02 University of Kansas
Radar Systems and Remote Sensing
Laboratory
Windvector
Measurements over
the Ocean
Radar at 14 GHz.
Concept developed at
KU.
USA, Europe and
Japan are planning
to launch satellites
to obtain data
continuously.
11/18/02 University of Kansas
Radar Systems and Remote Sensing
Laboratory
Founded in 1964.
4 Faculty members, 20 Graduate students - Ph. D & M.S.
4-6 Undergraduate students, 2 Staff
Now satellites based on concepts developed at RSL are in
operation.
NSCAT, QUICKSCAT- Radars to measure ocean surface winds.
ADEOS-2 (JAPAN), Europeans Met Office is planning to launch
satellite to support operational applications.
ScanSAR-
Radarsat- Canadian satellite
Envisat - European
SRTM -Shuttle Radar Topography Mission.Radar Systems
and Remote Sensing Laboratory
11/18/02 University of Kansas
Radar Systems and Remote Sensing
Laboratory
• Shuttle Radar Topography
Mission (SRTM)
– to collect three-
dimensional
measurements of the
Earth's surface.
– Acquired data to obtain
the most complete
near-global mapping of
our planet's topography
to date.
– This would not have
been possible without
ScanSAR operation---
concept developed at
KU.
11/18/02 University of Kansas
ITTC– Information Technology &
Telecommunication Center
• Communications academic emphasis and
research programs established in 1983.
• Now RSL is a part of the Center
• Graduated students
– degrees in EE, CS, CoE, Math
• 29 faculty, 15 staff researchers, 6 Center
staff
• Current student population ~ 130
– ~ 13 Ph.D., ~81 M.S., ~37 B.S.
11/18/02 University of Kansas
EM Spectrum
• Microwave region
• 300 MHz – 30 GHz.
Millimeter wave
• 30 GHz – 300 GHz.
IEEE uses a different
definition
• 300 MHz – 100 GHz
11/18/02 University of Kansas
Microwave Remote Sensing: Principles and
Applications.
• Advantages
– Day/night coverage.
– All weather except during
periods of heavy rain.
– Complementary
information to that in
optical and IR regions.
• Disadvantages
– Data are difficult to
interpret.
– Coarse resolution except
for SAR.
11/18/02 University of Kansas
Microwave Remote Sensing— history
• US has a long history in Microwave Remote Sensing.
– Clutter Measurement program after the WW-II.
• Ohio State University collected a large data
base of clutter on variety of targets.
– Earnest studies for the remote sensing of the
earth can be considered to have began 1960s.
• In 1960s NASA initiated studies to investigate
the use of microwave technology to earth
observation.
11/18/02 University of Kansas
Microwave Remote Sensing— history
• The research NASA and other agencies initiated resulted in:
– Development of ground-based and airborne sensors.
– Measurement of emission and scattering characteristics of
many natural targets.
– Development of models to explain and understand measured
data.
– Space missions with microwave sensors.
• NIMBUS
– Radiometers.
• SKYLAB
– Radar and Radiometers
11/18/02 University of Kansas
Microwave Remote Sensing
• Radar Applications
– Radio Detection and
Ranging. Civilian
Military
Navigation and Navigation and
– Texts: tracking tracking
• Skolnik, M. I., Search and
Search and
Introduction to Radar
surveillance
surveillance
Systems, McGraw Hill, Imaging &
1981. Mapping Imaging &
Mapping
• Stimson, G. W., Weather
Introduction to Airborne Sounding Weather
Radar, SciTech Probing
Publishing, 1998. Proximity fuses
Remote sensing
Counter measures
11/18/02 University of Kansas
Review – EM theory and Antennas
• Propagation of EM H J
D
waves is governed by t
Maxwell equations. E
B
t
.B 0
• For time-harmonic
variation we can .D
write the above H J j E
equations as E j H
.B 0
.D
11/18/02 University of Kansas
EM Theory
• Helmholtz Equation E 2E 0
2
– From the four H 2 H 0
2
Maxwell equations, where
we can derive vector
Helmholtz equations 2 Ex 2 Ex 2 Ex
2 Ex 0
x 2
y 2
z 2
2Ey 2Ey 2Ey
– For each component 2Ey 0
x 2
y 2
z 2
of E and H field we
2 Ez 2 Ez 2 Ez
can write a scalar x 2
y 2
z 2
2 Ez 0
equation
11/18/02 University of Kansas
Uniform plane wave
Amplitude and phase are constant on
planes perpendicular to the direction of
propagation.
TEM case– no component in the direction
of propagation.
For a TEM wave propagating in z direction
Ez = 0 and Hz =0
Ex(z,t) = Eo e-αz Cos(ωt-jβz)
11/18/02 University of Kansas
EM theory
• α and β are j j j
determined by For a loss - loss medium
material properties.
2
• Materials are r
Fresh wate ice, dry snow and
classified as dry soil are examples of low - loss media.
For a conductor
insulators and
conductors
2
–
11/18/02 University of Kansas
EM Theory
• Reflection and
refraction θi θr
– Whenever a wave
impinges on a
dielectric interface, θt
part of the wave will
be reflected and
remaining will be
transmitted into the
lower medium.
11/18/02 University of Kansas
EM Theory--Scattering
• Microwave Scattering from a
distributed target depends on
– Dielectric constant.
– Surface roughness.
– Internal structure.
• Homogeneous
• Inhomogeneous
– Wavelength or Frequency.
– Polarization.
11/18/02 University of Kansas
Microwave Scattering
• Surface scattering θi
θr
– A surface is classified as
smooth or rough by
comparing its surface Smooth surface
height deviation with
wavelength.
• Smooth h 2 fdmax For a radar withf p 1500 Hz
3x108
R un 100 km
2 x1500
c p
r , r 150m for p 1 s
2
11/18/02 University of Kansas
Radar—Principle
• Radar equation • For a monostatic radar
• GT = GR
PT • Radar sensitivity is determined
by the minimum detectable
GT R signal set by the receiver noise.
• No = kTBF
Power density at the target is given byP
PG
• F= noise figure
Pd T T
• Signal-to-noise ratio
4R 2
Target with radar crosssection, , intercepts
a part of this signal and reradiates
in the direction of the radar.
PG
Pdr T T
4R 2 S P P T GT 2
2
r
N N o ( 4 ) 3 R 4 KTBF
Reradiated power incident on the antenna is given by
PG 1
Pri T T
4R 2 4R 2
The receive antenna with an effectiveaperture, Ae, incident signal and it is given by P T GT2 2
PG Ae Rm ax 1
Pr T T 4 S
4R 2 4R 2 (4 ) 3 KTBF
P G G 2 N
Pr T T 3R 4
(4 ) R
4A
where GR 2 e
11/18/02 University of Kansas
Microwave Remote Sensing
• Radar cross section
characterizes the 2
size of the object as
Es
Lim R 4R 2
seen by the radar.
2
Ei
Where
Es = scattering field
Ei = incident field
r r 2
11/18/02 University of Kansas
Radar Equation
• A distributed target oA
contains many o scattering coefficient
scattering centers
A Illu min ated area
P T GT 2 0 A
2
within the Pr
(4 ) 3 R 4
illuminated area. It e a
is characterized by o
R
radar cross section
per unit area, which
is refereed to as
scattering
A
R cos( 0 ) tan( o e ) tan( o e ) R tan( a )
2 2 2 2
If 0 1 & 1
coefficient A
R2e a
4
11/18/02 University of Kansas
Radar Equation
P T GT 2 0 R e R a
2
Pr
( 4 ) 3 R 4 4
P T GT 2 0 e a
2
Pr
( 4 ) 2 R 2 16
For a distributed power received falls off as 1/R2
For a point target power received falls off as 1/R4
11/18/02 University of Kansas
Antenna Array
R1 Ro d sin
• Let us consider
R d sin
2
d sin
simple array j 2R0
Et Eo e e
j
2 ( Ro d sin
consisting of
d sin
j
2R0
j j d sin j d sin
Et Eo e
e e e
isotropic radiators.
j
2R0
j
d sin )
d sin
Et 2 Eo e
e
cos )
2d sin
Et Eoi cos
i
R1 If we increase from 0 to 90 degrees
and reduce the resulting expression.
sinx
Et
x
Ro
d
P
11/18/02 University of Kansas
Antenna Array
R1 Ro d sin
• Let us consider
R d sin
2
d sin
simple array j 2R0
Et Eo e e
j
2 ( Ro d sin
consisting of
d sin
j
2R0
j j d sin j d sin
Et Eo e
e e e
isotropic radiators.
j
2R0
j
d sin )
d sin
Et 2 Eo e
e
cos )
2d sin
Et Eoi cos
i
R1 If we increase from 0 to 90 degrees
and reduce the resulting expression.
sinx
Et
x
Ro
d
P
11/18/02 University of Kansas
Microwave Remote Sensing: Principles and
Applications— History
• Active Microwave sensing
– Studies related to active sensing of the
earth beagn in 1960s.
• Clutter studies
• SkYLab – radar altimeter and scatterometer in
1960s
• SEASAT in 1978
• ERS-1, JERS-1, ERS-2, RADARSAT, GEOSAT,
Topex-Posoidon
11/18/02 University of Kansas
Active Sensors – Radar Altimeter
• Radar altimeter is a short pulse radar
used for accurate height measurements.
– Ocean topography.
– Glacial ice topography
– Sea ice characteristics
• Classification and ice edge
• Vegetation
•http://topex-www.jpl.nasa.gov/technology/images/P38232.jpg
11/18/02 University of Kansas
Radar Altimeter
• Missions
Satellite Radar Altimeters
Mission Frequency Accuracy Period
SKYLAB Ku 10 m 1973
GEOS Ku 1-5 M 1976
SEASAT Ku ~1 m 1978
GEOSAT Ku 10 CM 1985-1990
ERS-1 Ku < 10 cm 1992-1998
TOPEX C &Ku < 10 cm 1992-
ERS-2 Ku < 10 cm 1996-
GFO Ku <10 cm 1998-
ENVISAT Ku &S <10 CM 2001-
Jason-1 Ku &C <10 cm 2000-
CRYOSAT and other
missions Ku Few cm 2003-
11/18/02 University of Kansas
Radar Altimeter— Waveform
• Satellite altimeters operate
in pulse-limited mode.
R2 H 2 Y 2
c
RH H
2
c
2
H H Y
2 2 Ct/2
2
c
H
2
c
H 2 cH ( ) 2 H 2 Y 2
2
Y cH
R Re solution 2Y 2 cH
Amplitude
For H 800 km, 3.3 ns
R 1.7km
Time
11/18/02 University of Kansas
Radar Altimeter
• A short pulse radar
– Uses pulse compression to obtain fine range
resolution or height measurement.
– Range measurement uncertainty of a pulse radar.
c
r
S
2B 2
N
For example B 300 MHz, S/N 100
r 3.5 cm
11/18/02 University of Kansas
Radar altimeter
• Other sources of errors
– Atmospheric delays
– Troposheric delays.
– EM bias
– Pointing errors
– Orbit errors
– Accuracies of few cms are
being achieved with new
generation sensors.
• Dual-frequency
• Water vapor— Resti et al, “The Envisat Altimeter System RA-2,”ESA
radiometers Bulletin 98, June 1999
• GPS – orbit determination
• Calibration.
sigma=5.5 cm
11/18/02 University of Kansas
Radar Altimeter—typical system
Resti et al, “The Envisat Altimeter System RA-2,”ESA Bulletin 98, June 1999
11/18/02 University of Kansas
Radar Altimeter
• Waveform analysis
– Time delay is measured
very accurately and
converted into
distance.
– Spreading of the pulse
is related to SWH.
– Scattering coefficient
can be obtained by
determining the power.
Resti et al, “The Envisat Altimeter System
RA-2,”ESA Bulletin 98, June 1999
11/18/02 University of Kansas
Radar Altimeter- typical system
• Block diagram of Envisat RA
Resti et al, “The Envisat Altimeter System RA-2,”ESA Bulletin 98, June 1999
11/18/02 University of Kansas
Active sensors
• Scatterometer
– Scatter o Meter – A calibrated radar used to
measure scattering coefficient.
– They are used to measure radar backscatter as a
function of incidence angle.
– Ground and aircraft-based scatterometers are
widely used.
– Experimental data on variety of targets to support model
and algorithm development activities.
» Developing algorithms for extracting target
characteristics from data.
» Understanding the physics of scattering to develop
empirical or theoretical models.
» Developing target classification algorithms
11/18/02 University of Kansas
Active sensors— Scatterometers
• Wide range of applications
– Wind vector measurements
– Sea and glacial ice
– Snow extent.
– Vegetation mapping
– Soil moisture
• Semi-arid or dry areas.
11/18/02 University of Kansas
Microwave Remote Sensing— Atmosphere
and Precipitation
• Global precipitation mission
– Will consist of a primary spacecraft and a
constellation.
• Primary Spacecraft
– Dual-frequency radar.
» 14 and 35 GHz.
– Passive Microwave Radiometer
– Constellation Spacecraft
• Passive Microwave Radiometer
11/18/02 University of Kansas
Microwave Remote Sensing—Active
Sensors
Imaging Radars
Imaging Radars & Scatterometers
• Imaging Radars
• Real Aperture Radar (RAR)
• Synthetic Aperture Radar (SAR)
• Widely used for military and civilian
applications.
• RAR
• Thin long antenna mounted on the side of an
aircraft.
11/18/02 University of Kansas
Imaging radars
• RAR • RAR geometry
– Resolution is
determined by
antenna beamwidth in
the along track
direction r R k
a
R
D
a
k weighting factor
– Pulse width in the
cross-track direction
c
rc
2 sin( )
11/18/02 University of Kansas
Imaging radars
• For a radar operating
at f=10 GHz with a 3-m 10000x0.03
ra 0.8 80 m
long antenna in the 3
along track direction rc
3x108 x0.5 x106
106 m
and 0.5 us pulse, 2 sin(45)
R 100 km
resolution at 45 degree
100000x0.03
incidence and range of ra 0.8
3
800 m
10 km is given by 3x108 x0.5 x106
rc 106 m
• Assume k=0.8 2 sin(45)
11/18/02 University of Kansas
Imaging Radars: RAR
RARs were used
• Resolution until 1990s.
They are replaced
by SARs.
Resolution should
1/20 about the
dimensions of the
target we want to
recognize
MRS: vol. II, Ulaby, Moore and Fung
11/18/02 University of Kansas
SAR
• Synthetic Aperture Radar
• Use the forward motion of an aircraft or a
spacecraft to synthesize a long antenna.
• Satellite SARs
• ERS-1, ERS-2, RADARSAT, ENVISAT, JERS-1,
SEASAT, SIR-A,B& C.
• Applications
• Ocean wave imaging
• Oil slick monitoring
• Sea ice classification and dynamics
• Soil moisture
• Vegetation
• Glacial ice surface velocity
11/18/02 University of Kansas
SAR
• We can use a small physical antenna
• For focused SAR resolution is
independent of
• Wavelength
• Range
• Best possible resolution is L/2
• Where L= length of the physical antenna
11/18/02 University of Kansas
RF Spectrum
Microwave Radiometry covers a range of frequencies.
Soil Atmospheric
Atmospheric
Moisture Ocean Surface Wind Water Vapor Cloud Ice
Temperature
1-3 GHz 19, 22 GHz 22, 24, 92, 150, 325, 448, 643 GHz
54, 118 GHz
Resolution / Polarimetry 183 GHz High frequency
Accuracy
aperture Accuracy
30 cm 3 cm 3 mm 0.3 mm
1 GHz 10 GHz 100 GHz 1000 GHz
Atmospheric
Sea Surface Salinity Precipitation
Sea Ice Chemistry
1-3 GHz 11, 31,37,89 GHz
37 GHz 190, 240, 640,
Receiver sensitivity/ Frequent global
Polar coverage 2500 GHz
stability coverage
High frequency
Hartley, NASA
L band S band C band X band Ku/K/Ka band Millimeter Submillimeter
11/18/02 University of Kansas
Microwave Radiometers— theory
• Planck’s Law of radiation
2hc 2 1
s ( , T )
5 ch
e kT
1
• Where S(λ,T) =Intensity of
radiation in w/m2
• T = temperature in Kelvins
• h = Planck’s constant, 6.625 ×
10-34 J·s Rayleigh Jeans Approx
• c = velocity of propagation
ch
kT
m/s
2ckT
S ( , T )
4
• k = Boltzmann constant,
1.380 × 10-23 J/K
• λ = wavelength, m
11/18/02 University of Kansas
Microwave Radiometer
• At microwave frequencies radiation
intensity is directly proportional to the
temperature.
• For gray bodies
– Pa = kTb B
– k =Boltzman constant, B = bandwidth, Hz.
– Tb = Brightness temperature, K
– Tb =e Tphy
– e = Emissivity of the object or media
11/18/02 University of Kansas
Microwave Radiometer
Two basic types of radiometers
– Total power radiometer
• Highest sensitivity
– Switching-type radiometers and its variants.
TTotal
T
B in
• Typical total power radiometer where Ttota l Ta Tsy s
B bandwidth
Mixer
Square-law det in int egration time
LNA IF Amp
Bandpass Filter Integrator
B 6 MHz, in 1s
Ttotal 500 K
Local Oscillator
T 0.2 K
11/18/02 University of Kansas
Microwave Radiometer
• Dicke or Switching-type radiometer
– Any fluctuations in gain of the receiver will
reduce radiometer sensitivity.
– To eliminate system effects, Dicke
developed switching type radiometer.
• It consists of switch and a synchronous
detector. The input is switched between the
antenna and noise source. If the injected noise
power is equal to input signal power, the effect
of gain fluctuations is eliminated.
11/18/02 University of Kansas
Microwave Radiometer
• Typical Dicke-type radiometer
Modulator
Mixer Bandpass Filter
-
LNA Diff Amp
+
L IF Amp +
Noise
source
Local Oscillator
If the duty cycleis 50%, integration time is reduced by 50%
1.4Ttotal
T
B in
11/18/02 University of Kansas
RF Radiometry Characteristics
Moden Radiometer
Digital processor
To eliminate down conversion process
Antenna
Receiver
digital
multiplexer/ detector/
low noise mixer processor/
spectrometer digitizer
amplifier correlator
LO
Hartley, NASA
scan
11/18/02 University of Kansas
Microwave Remote Sensing
• Research and application of
microwave technology to remote
sensing of
– Oceans and ice
– Solid earth and Natural hazards..
– Atmosphere and precipitation.
– Vegetation and Soil moisture
11/18/02 University of Kansas
Microwave Remote Sensing— Ocean and
Ice
• Winds
– Scatterometer.
• Quickscat, Seawinds
– Polarimetric radiometer
• Ocean topography
– Radar altimeters
• Ocean salinity
– AQUARIUS
• Radiometer and radar combination.
– Radar to measure winds for correcting for the effect
of surface roughness.
11/18/02 University of Kansas
Ocean Vector Winds— Scatterometers
Scatterometers send microwave pulses to the
Earth's surface, and measure the power scattered
back. Backscattered power over the oceans
SeaWinds
depends on the surface roughness, which in turn
QuikScat
depends on wind speed and direction.
QuikScat
• Replacement mission for NSCAT, following loss of ADEOS
• Launch date: June 19, 1999
SeaWinds
• EOS instrument flying on the Japanese ADEOS II Mission
• Launch date: December 14, 2002 ????
Instrument Characteristics of QuikScat and SeaWinds
• Instrument with 120 W peak (30% duty) transmitter at 13.4
GHz, 1 m near-circular antenna with two beams at 46o and 54o
incidence angles
Advanced sensors– larger aperture
antennas.Passive polarimetric sensors.
11/18/02 University of Kansas
Courtesy: Yunjin Kim, JPL
Ocean Topography Missions
The most effective measurement of ocean currents
from space is ocean topography, the height of the sea
surface above a surface of uniform gravity, the geoid.
TOPEX/Poseidon and Jason-1
• Joint NASA-CNES Program
– TOPEX/Poseidon launched on August 10, 1992
– Jason-1 launched on December 7, 2001
• Instrument Characteristics
– Ku-band, C-band dual frequency altimeter
– Microwave radiometer to measure water vapor
– GPS, DORIS, and laser reflector for precise orbit determination
• Sea-level measurement accuracy is 4.2 cm
• TOPEX/Poseidon & Jason-1 tandem mission for high resolution ocean
topography measurements
The priority is to continue the measurement
with TOPEX/Poseidon accuracy
on a long-term basis for climate studies.
Courtesy: Yunjin Kim, JPL TOPEX/Poseidon Ocean topography
11/18/02 University of Kansas of the Pacific Ocean during El Niño
and La Niña.
Ocean Surface Topography Mission
An Experimental Wide-Swath Altimeter
By adding an interferometric radar system to a conventional radar altimeter
system, a swath of 200 km can be achieved, and eddies can be monitored over
most of the oceans every 10 days. The design of such a system has
progressed, funded by NASA’s Instrument Incubator Program. This
experiment is proposed to the next mission, OSTM (Ocean Surface
Topography Mission)
South America
Courtesy: Yunjin Kim, JPL
11/18/02 University of Kansas
Global Ocean Salinity
• Aquarius (JPL, GSFC, CONAE)
• ESSP-3 mission in the risk
mitigation phase
• First instrument to measure global
ocean salinity
– Passive and active microwave
instrument at L-band
– Resolution
• Baseline 100km, Minimum 1 week of salinity measurements from space
200km
– Global coverage in 8 days
– Accuracy: 0.2 psu
– Baseline mission life: 3
years
11/18/02 University of Kansas
Courtesy: Yunjin Kim, JPL 100 yrs of salinity measurements by ship
SRTM (Shuttle Radar Topography Mission)
• C-band single pass interferometric SAR for
topographic measurements using a 60m
mast
• DEM of 80% of the Earth’s surface in a
single 11 day shuttle flight
– 60 degrees north and 56 degrees south
latitude
– 57 degrees inclination
• 225 km swath
• WGS84 ellipsoid datum
• JPL/NASA will deliver all the processed data
• Partnership between NASA and NIMA to NIMA by January 2003
(National Imagery and Mapping Agency) • Absolute accuracy requirements
•X-band from German and Italian space – 20 m horizontal
agencies – 16 m vertical
• The current best estimate of the SRTM
accuracy is
Courtesy: Yunjin Kim, JPL
• 10 m horizontal and 8 m vertical
11/18/02 University of Kansas
L-band InSAR Technology
• Interferometric Synthetic Aperture Radar
(InSAR) can measure surface
deformation (mm-cm scale) through
repeated observations of an area
• L-band is preferable due to longer
correlation time due to longer
wavelength (24cm) Surface deformation due to Hector Mine
• Solid Earth Science Working Group Earthquake using repeat-pass InSAR data
recommended that
• In the next 5 years, the new space
mission of highest priority for solid-
Earth science is a satellite
dedicated to InSAR measurements
of the land surface at L-band
InSAR velocity difference indicates a 10%
increase in ice flow velocity from 1996 to
2000 on Pine Island Glacier
11/18/02 University of Kansas [Rignot et al., 2001]
Microwave Remote Sensing— Soil
Moisture.
Southern Great Plains Hydrology Experiment (SGP97)
Surface Soil Moisture Derived From Remotely Sensed Microwave Data
37.0
June 30 July 1
Radar
Lamont Lamont
36.5
Soil Moisture (%)
50
50
Pol: VV, HH & HV
36.0
ElReno ElReno
35.5 OklahomaCity OklahomaCity
40
40
Chickasha Chickasha
Res – 3 and 10 km
Latitude (Degrees)
35.0
SGP’97
30
30
July 2 July 3
Lamont Lamont
36.5
20
20
Radiometer 36.0
ElReno ElReno
10
10
OklahomaCity OklahomaCity
35.5
Pol: H, V 35.0
Chickasha Chickasha
00
-98.5 -98.0 -97.5 -98.0 -97.5 -97.0
Longitude (Degrees)
Res =40 km, NASA Land Surface Hydrology Program
dT= 0.64º K Courtesy: Tom Jackson, USDA
• HRDROS
– Back-up ESSP mission for global soil moisture.
• L-band radiometer.
• L-band radar.
11/18/02 University of Kansas
Microwave Remote Sensing— Atmosphere and
Precipitation CloudSAT
Salient Features
NASA ESSP mission
First 94 GHz radar space borne system
Co-manifested with CALIPSO on Delta launch vehicle
Flies Formation with the EOS Constellation
Current launch date: April 2004
Operational life: 2 years
Partnership with DoD (on-orbit ops), DoE
(validation) and CSA (radar development)
Science
Measure the vertical structure of clouds and quantify their ice and water content
Improve weather prediction and clarify climatic processes.
Improve cloud information from other satellite systems, in particular those of Aqua
Investigate the way aerosols affect clouds and precipitation
Investigate the utility of 94 GHz radar to observe and quantify precipitation, in the
context of cloud properties, from space
11/18/02 University of Kansas
Courtesy: Yunjin Kim, JPL
Earth Science and RF Radiometery
Atmospheric chemistry
Precipitation
Microwave Sea surface temperature/
Radiometry Sea surface salinity
Applications.
Hartley, NASA
Ocean surface wind
Atmospheric temperature, humidity, and clouds Soil moisture
11/18/02 University of Kansas
Conclusions
• A brief overview of microwave remote
sensing principles and applications.
• Opportunities for research and
education.
– Science
– Technology
11/18/02 University of Kansas
SAR—Principle
• SAR can explained using the concept
of a matched filter or antenna array.
Ro
11/18/02 University of Kansas
SAR— Principle
• Unfocussed SAR
4Ro
• No phase corrections are made. o
4R
N
2
l l2
R R0 Ro
2
Ro 2 8 Ro
4l 2
d N o
r 8 Ro 4
Ro
l
2
11/18/02 University of Kansas
SAR— Principle
• Focussed SAR
0.5
x2
R R
x 2 Ro 1 2
2
o R
x x 2
o
R Ro
2 Ro
Ro 2 x2 2x 2
d ( x) 2
2 Ro Ro
2x 2
e
Thus we need to correct th phase by -
Ro
to make all the vectorsadd up
11/18/02 University of Kansas
SAR— Principle
• Resolution
The 3 - dB beamwidth of an uniformly illuminate d real
aperture of length, D, is given by ar 0.88
D
For synthetic aperture of length, Leff , as 0.44
Lef
4 - dB beamwidth are given by
Ro
ar , as 0.5 & Lef
D Lef D
Ro D
Along track resolution, ra as Ro
2 Le f 2
11/18/02 University of Kansas