Urs Wegmüller, Maurizio Santoro, Charles Werner,Tazio Strozzi and Andreas Wiesmann

Gamma Remote Sensing, Gümligen, Switzerland

ESTIMATION OF ICE THICKNESS OF TUNDRA LAKES USING ERS – ENVISAT CROSS-

INTERFEROMETRY

This work was supported by ESA under contract 22526/09/I-LG.ERS and ASAR data copyright ESA (CAT 6744).

Motivation

ERS – ENVISAT Cross-Interferometry (EET-CInSAR)

Ice thickness estimation methodology

Results over Kolyma area, Siberia

Results over Mackenzie area, Canada Conclusions

Outline

Significant interest in information on Tundra lakes and frozen rivers

Freezing of tundra lakes and rives relevant for several applications reaching from ice road planningto environmental consideration and climate change

One important parameter is the ice-thickness

Space-borne SAR has shown significant potential already over tundra areas

ERS – ENVISAT Cross-Interferometry (EET-CInSAR) data available over tundra areas

Coherence over frozen lakes is usually high and phase looks different from surrounding, indicating some potential to derive information

Motivation

EET Cross-Interferogram over Kolyma River Delta area(20-Jan-2009, dt= 28min., B⊥= 2130m, dDC= 139Hz)

How can we interpret the interferometric phase?

Can we retrieve relevant information?

EET Cross-Interferometry (EET-CInSAR)Sensor parameters

Parameter ERS-2 SAR ENVISAT ASAR IS2 VV

SAR_center_frequency 5.300 GHz 5.331 GHz

Polarization VV VV

nominal_antenna_look_angle 20.350 deg. 20.138 deg.

Orbits 35-day repeat cycles

Same as ERS-2, ~28’ ahead of

ERS-2

pulse_repetition_frequency 1679.9 Hz 1652.42 Hz

azimuth_pixel_spacing 3.97 m 4.04 m

Doppler spectra nominal Doppler spectra overlap strongly

chirp_bandwidth 1.555e+07 Hz 1.600e+07 Hz

ADC_sampling_frequency 1.896e+07 Hz 1.921e+07 Hz

range_pixel_spacing 7.90 m 7.80 m

EET Cross-Interferometry (EET-CInSAR)Orbit and CInSAR geometry

Interferometric phase: (1)

Phase components: (2)(case f1 = f2)

Case f1 ≈ f2 :

1) calculate using (1) with flat ellipsoid2) apply (2) using

EET Cross-Interferometry (EET-CInSAR)CInSAR phase

)44

( 11

22 r

c

fr

c

f ππφ −−=

noisepathdisporb rhr

B φφλπ

θλπφφ +++

⋅+= ⊥ 4

sin

4

21

2

ff

c

+=λ

orbφ

For Bperp = 2km:

Height ambiguity: 4.70m

EET Cross-Interferometry (EET-CInSAR)CInSAR phase to height sensitivity

⊥⊥ ⋅=°⋅⋅

= Bm

radB

mmdh

d2

0006688.023sin000'852056439.0

4πφ

m

rad

dh

d34.1=φ

EET CInSAR DEM Generation: Po Delta

Topographic phase is shown

EET pair on 31-Dec-2008dtime 28 min.B⊥ 1754m dDC 958Hz ambiguity height 5.4m Area shown 96km x 112km

Refraction:

“Effective height difference:

Ice thickness: ; for :

INSAR phase model for frozen lake

'

sinsin 1

2εθ

θ =

2

11 cos

cos'cos

θθεθ iceeff hlh ==∆

1

12

cos'

sin'

θεθε −

∆= effice hh 60.0*effice hh ∆=.deg231 =θ

Kolyma River (20-Jan-2009, B⊥=2130m, dDC= 139Hz)

ENVISAT backscattering Cross-interferogram phase

Kolyma River (20-Jan-2009, B⊥=2130m, dDC= 139Hz)

ENVISAT backscattering Cross-interferogram phase

bottom-fast

not frozento ground

Kolyma River (20-Jan-2009, B⊥=2130m, dDC= 139Hz)

ENVISAT backscattering Ice thickness maps bottom-fast

not frozen to ground

partially bottom-fast

Height below reference level (coastal height)

Bottom-fast ice lake floor topography

Mackenzie River (10-Mar-2009, B⊥=2247m, dDC=344Hz)

ENVISAT backscattering Cross-interferogram phase

Mackenzie River (10-Mar-2009, B⊥=2247m, dDC=344Hz)

ENVISAT backscattering

ection 1, incl. points measured in 27.2-9.3.2009 by J.J. van Sanden et al. 2009

Mackenzie River (10-Mar-2009, B⊥=2247m, dDC=344Hz)

Cross-interferogram phase

ection 1, incl. points measured in 27.2-9.3.2009 by J.J. van Sanden et al. 2009

+3A

+3C

+3B

+ + *

+

* h=0 ref. used

Mackenzie River (10-Mar-2009, B⊥=2247m, dDC=344Hz)

ffective height transect (negative values correspond to ice thickness)

: value from J.J. van Sanden et al., 2009

* h=0 ref. used

*

Mackenzie River (10-Mar-2009, B⊥=2247m, dDC=344Hz)

ENVISAT backscattering

ection 2, incl. points measured in 27.2-9.3.2009 by J.J. van Sanden et al. 2009

Mackenzie River (10-Mar-2009, B⊥=2247m, dDC=344Hz)

Cross-interferogram phase

ection 2, incl. points measured in 27.2-9.3.2009 by J.J. van Sanden et al. 2009

+8A

+8B

+

+ *

* h=0 ref. used

Mackenzie River (10-Mar-2009, B⊥=2247m, dDC=344Hz)

ffective height transect (negative values correspond to ice thickness)

: value from J.J. van Sanden et al., 2009

* h=0 ref. used

*

Conclusions

EET pairs with 2km and 28’ time interval coherence often high over frozen lakes high sensitivity of CINSAR to ice thickness (hamb,ice ≅ 3m)

From unwrapped CINSAR phases relative to a point on the coast representing the lake(-ice) surface level, ice thickness maps can be derived (for highly transparent fresh-water ice)

In the case of bottom-fast ice (i.e. ice frozen to the ground) this corresponds to the mapping of the lake floor topography

For frazil ice (snow/water mixture) and for ice covered by wet snow or water, and for sea ice the dominant scattering is not from the ice/water or ice/lake ground interface, so that the presented methodology is not applicable

The comparison with a few in-situ measured ice thickness values confirmed the potential

Outlook

In 2007/08 and 2008/09 suitable EET pairs were acquired over quite many northern sites, so that the presented methodology may be applied elsewhere

Acquiring further EET pairs after Oct. 2010 is not foreseen