geogg141 principles & practice of remote sensing (pprs) radar iii: applications revision

UCL DEPARTMENT OF GEOGRAPHYUCL DEPARTMENT OF GEOGRAPHY

GEOGG141Principles & Practice of Remote Sensing (PPRS) RADAR III: ApplicationsRevision

Dr. Mathias (Mat) DisneyUCL GeographyOffice: 113, Pearson BuildingTel: 7670 0592Email: [email protected]/~mdisney

UCL DEPARTMENT OF GEOGRAPHY

RECAP


Observations of forests...

• C-band (cm-tens of cm)– low penetration depth, leaves / needles / twigs

• L-band– leaves / branches

• P-band– can propagate through canopy to branches, trunk and ground

• C-band quickly saturates (even at relatively low biomass, it only sees canopy); P-band maintains sensitivity to higher biomass as it “sees” trunks, branches, etc

• Low biomass behaviour dictated by ground properties


• Surfaces - scattering depends on moisture and roughness• Note - we could get penetration into soils at longer wavelengths

or with dry soils (sand)

• Surfaces are typically– bright if wet and rough– dark if dry and smooth

• What happens if a dry rough surface becomes wet ?

• Note similar arguments apply to snow or ice surfaces.

• Note also, always need to remember that when vegetation is present, it can act as the dominant scatterer OR as an attenuator (of the ground scattering)


EasternSahara desert

SIR-APenetration 1 – 4 m

Landsat


Safsaf oasis, Egypt

SIR-C L-band 16 April 1994Landsat

Penetration up to 2 m


Single channel data• Many applications are based on the operationally-available

spaceborne SARs, all of which are single channel (ERS, Radarsat, JERS)

• As these are spaceborne datasets, we often encounter multi-temporal applications (which is fortunate as these are only single-channel instruments !)

• When thinking about applications, think carefully about “where” the information is:-– scattering physics– spatial information (texture, …)– temporal changes


Multi-temporal data• Temporal changes in the physical properties of regions in

the image offer another degree of freedom for distinguishing them but only if these changes can actually be seen by the radar

• for example - ERS-1 and ERS-2:-– wetlands, floods, snow cover, crops– implications for mission design ?

• ALOS-PALSAR (2005-2011) revisits


Wetlands in Vietnam - ERS

Oct 97 Jan 99 18 Mar 99 27 May 99

Sept 99 Dec 99 Jan 00 Feb 00


Wetlands...


SIR-C (mission 1 left, mission 2 centre, difference in blue on right)


Floods...

Maastricht

A two date composite of ERS SAR images

30/1/95 (red/green)

21/9/95 (blue)


Snow cover...Glen Tilt - Blair Atholl

ERS-2 composite

red = 25/11/96

cyan=19/5/97

Scott Polar Research Institute


Agriculture

Gt. Driffield

Composite of 3 ERS SAR images from different dates


OSR - Oil seed rapeWW - Winter wheat


ERS SAREast Anglia


Radar modelling

• Surface roughness• Volume roughness• Dielectric constant ~ moisture• Models of the vegetation volume, e.g. water cloud model

of Attema and Ulaby, RT2 model of Saich

Multitemporal SHAC radar imageBarton Bendish


Water cloud model

A – vegetation canopy backscatter at full cover

B – canopy attenuation coefficient

C – dry soil backscatter

D – sensitivity to soil moisture

σ0 = scattering coefficientms = soil moistureθ = incidence angleL = leaf area index

Vegetation


Values of A, B, C, D

Parameter Value Units / description

A -10.351 dB

B 1.945 Fractional canopy moisture

C -23.640 dB

D 0.262 Fractional soil moisture


Simulated backscatter

r2 = 0.81


Canopy moisture

r2 = 0.96


Applications

• Irrigation fraud detection• Irrigation scheduling• Crop status mapping, e.g.

disease, water stress


Multi-parameter radar

• More sophisticated instruments have multi-frequency, multi-polarisation radars, with steerable beams (different incidence angle)

• Also, different modes– combinations of resolutions and swath widths

• SIR-C / X-SAR• ENVISAT ASAR, ALOS PALSAR,...


Flevoland April 1994

(SIR-C/X-SAR)

(L/C/X composite)

L-total power (red)

C-total power (green)

X-VV (blue)


Thetford, UK

AIRSAR (1991)

C-HH


Thetford, UK

AIRSAR (1991)

multi-freq composite


Thetford, UK

SHAC (SAR and Hyperspectral Airborne Campaign)http://badc.nerc.ac.uk/view/neodc.nerc.ac.uk__ATOM__dataent_11742960559518010

Disney et al. (2006) – combine detailed structural models with optical AND RADAR models to simulate signal in both domainshttp://www.sciencedirect.com/science/article/pii/S0034425705003445Drat optical model + CASM (Coherent Additive Scattering Model) of Saich et al. (2001)

Coherent RADAR modelling


Coherent RADAR modelling

Thetford, UK

SHAC (SAR and Hyperspectral Airborne Campaign)http://badc.nerc.ac.uk/view/neodc.nerc.ac.uk__ATOM__dataent_11742960559518010

Disney et al. (2006) – combine detailed structural models with optical AND RADAR models to simulate signal in both domainshttp://www.sciencedirect.com/science/article/pii/S0034425705003445Drat optical model + CASM (Coherent Additive Scattering Model) of Saich et al. (2001)


Optical signal with age for different tree density (HyMAP optical data)


Coherent (polarised) modelled RADAR signal (CASM)


OPTICAL

RADAR


An ambitious list of Applications...

• Flood mapping, Snow mapping, Oil Slicks• Sea ice type, Crop classification,• Forest biomass / timber estimation, tree height• Soil moisture mapping, soil roughness mapping / monitoring• Pipeline integrity• Wave strength for oil platforms• Crop yield, crop stress• Flood prediction• Landslide prediction


CONCLUSIONS• Radar is very reliable

because of cloud penetration and day/night availability

• Major advances in interferometric SAR

• Should radar be used separately or as an adjunct to optical Earth observation data?

ALOS (RIP)


Revision• Exam: 3 hrs, answer 4 from 7 (2 from Dietmar, 5 from me) • Types of question based on PREVIOUS material be similar

each year (not surprisingly!)– Planck function, orbital calculations, definitions of terms, pre-

processing stages– Factors controlling measured signal from vegetation across

vis/SWIR, or angular behaviour– RADAR principles eg RADAR equation, resolutions– Principles of SAR interferometry and applications– General questions - systems to address a given problem

• KEY: address that problem• Does Q give scope for moving beyond one platform or wavelength? If

so then DO SO…


Revision

• Types of question based on NEW material for 2011– LiDAR

• Principles of lidar remote sensing?• What is it good for and limitations?• Example applications

– Radiative Transfer modelling• Basis of RT model – building blocks?

– Structure, leaf scattering, soil scattering• Scalar RT equation

– what do terms mean?– How can we go about solving?


Revision problems: Planck’s Law

43

• Fractional energy from 0 to F0? Integrate Planck function

• Note Eb(,T), emissive power of bbody at , is function of product T only, so....

Tb

TTETd

TTETF

054

00

,,,,

Radiant energy from 0 to

Total radiant energy for =0 to =


Revision: Planck’s Law example

44

• Q: what fraction of the total power radiated by a black body at 5770 K fall, in the UV (0 0.38µm)?• Need table of integral values of F0

• So, T = 0.38m * 5770K = 2193mK• Or 2.193x103 mK i.e. between 2 and 3

• Interpolate between F0 (2x103) and F0 (3x103)

T (mK x103) F0(T)(dimensionless)

2 .0673 .2734 .4815 .6346 .7388 .85610 .91412 .94514 .96316 .97418 .98120 .986

193.0

232193.2

102103102,

338.00

338.00

338.0038.00

xFxFxFTF

193.0067.0273.0

067.0,38.00

TF

• Finally, F00.38 = 0.193*(0.273-0.067)+0.067 = 0.11

• i.e. ~11% of total solar energy lies in UV between 0 and 0.38m


• Orbital period for a given instrument and height? – Gravitational force Fg = GMEms/RsE

2

• where G is universal gravitational constant (6.67x10-11 Nm2kg2); ME is Earth mass (5.983x1024kg); ms is satellite mass (?) and RsE is distance from Earth centre to satellite i.e. 6.38x106 + h where h is satellite altitude

– Centripetal (not centrifugal!) force Fc = msvs2/RsE

• where vs is linear speed of satellite (=sRsE where is the satellite angular velocity, rad s-1)

– for stable (constant radius) orbit Fc = Fg – GMEms/RsE

2 = msvs2/RsE = ms s

2RsE2 /RsE

– so s2 = GME /RsE

3

45

Orbits: examples

From:http://csep10.phys.utk.edu/astr161/lect/history/kepler.html


• Orbital period T of satellite (in s) = 2/– (remember 2 = one full rotation, 360°, in radians)– and RsE = RE + h where RE = 6.38x106 m– So now T = 2[(RE+h)3/GME]1/2

• Example: geostationary altitude? T = ??– Rearranging: h = [(GME /42)T2 ]1/3 - RE

– So h = [(6.67x10-11*5.983x1024 /42)(24*60*60)2 ]1/3 - 6.38x106

– h = 42.2x106 - 6.38x106 = 35.8km

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Orbits: examples


• Example: polar orbiter period, if h = 705x103m– T = 2[(6.38x106 +705x103)3 / (6.67x10-11*5.983x1024)]1/2

– T = 5930.6s = 98.8mins• Example: show separation of successive ground tracks

~3000km– Earth angular rotation = 2/24*60*60 = 7.27x10-5 rads s-1 – So in 98.8 mins, point on surface moves 98.8*60*7.27x10-5 = .431 rads– Remember l =r* for arc of circle radius r & in radians– So l = (Earth radius + sat. altitude)* – = (6.38x106 +705x103)* 0.431 = 3054km

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Orbits: examples

geogg141 principles & practice of remote sensing (pprs) radar iii: applications revision

Documents

vietnam ers

example ers

single channel ers

glen tilt blair atholl

temporal datatemporal

multitemporal applications

canopy pband

mission design