IGARSS 2011

SAR Data for Subsurface Saline Lacustrine Deposits Detection and Primary

Interpretation on the Evolution of the Vanished Lop Nur Lake

Xiaolin Bian, Yun Shao, Huaze Gong

Institute of Remote Sensing Applications, Chinese Academy of Sciences

• Introduction

• Field Works and Analysis

• Polarimetric Analysis and Results

• Multi-source SAR Data Analysis

and Interpretation

• Conclusion

Outline

Introduction

RADARSAT-1

TM

ALOS-PALSAR

Introduction

located in east Tarim Basin in Xinjiang Uygur

Autonomous Region, northwest China 5350 km2 as reported less than 20 mm annual precipitation, over 3000

mm or more evaporation……. “Drought Pole” Concentration center for mineral salts famous Earth “Ear” Pattern

Introduction

Penetration ability for

SAR

Polarimetrictechnology

combination

Lop Nur penomenon

Field Works and Analysis

Field investigation routes and sampling pit locations.(A, B and C are field routes in 2006 in black line; I 、 II and III are field routes in 2008 in blue line; red dots are sampling locations of 2008 field trip, which are mainly analyzed in this report.)

Field Works and Analysis

Sample collection at sampling sites located on the bright strip (A) and dark strip (B) on SAR images.

Total 5 field trips ， 520 samples

6 lacustrine deposits samples were collected for each sampling site from surface to bottom of each sampling pit at different depths

Moisture, ion content, particle size, PH value, dielectric constants.

A B

Field Works and Analysis

Moisture

1 2 3 4 5 6

0

5

10

15

20

25

30

35

Moi

stur

e%

（）

No. of sampling sites from surface to subsurface

Moisture variation from surface to bottom of the lacustrine deposits at selected sampling pits

Field Works and Analysis

Subsurface scattering mechanism illustration

Polarimetric Analysis and Results

The co-polarization correlation

Co-polarization correlation analysis for bright and dark region(Length of radius is co-polarization correlation coefficient; scattered angle

of circumference stands for phase differences.)

Polarimetric Analysis and Results

Degree of Polarization

Degree of polarization for bright and dark regions

Regions PMax PMin p (p = PMax - PMin)

Bright I 0.74 0.46 0.28

Dark I 0.84 0.65 0.19

Bright II 0.75 0.48 0.27

Dark II 0.81 0.6 0.21

Bright III 0.71 0.41 0.3

Dark III 0.8 0.57 0.23

Polarimetric Analysis and Results

Degree of Polarization

0.71 0.72 0.73 0.74 0.75 0.76 0.77 0.78 0.79 0.80 0.81 0.82 0.83 0.840.18

0.20

0.22

0.24

0.26

0.28

0.30

bright region dark region

p

PMax

(PMax, p) of bright and dark region (The dot and dash line means boundary of different regions randomly.)

Polarimetric Analysis and Results

Shannon entropy (latest)

Shannon entropy for bright and dark regions

Polarimetric Analysis and Results

Shannon Entropy

Shannon entropy is a sum of two contributions related to intensity and polarimetry.

Shannon entropy and its intensity, polarimetric contributions maps

HH, VV and HV polarization amplitude maps of RADARSAT-2 data

Polarimetric Analysis and Results

Polarimetric decomposition

Polarimetric decomposition results in single scattering, dihedral scattering and multiple scattering with Cloude decomposition based on ALOS-PALSAR data.

Polarimetric Analysis and Results

Polarimetric decomposition

-2 0 2 4 6 8 10 12 14 16 18 20 22 24 2630

40

50

60

70

80

90

100

subsurface salinity %（ ） multiple scattering

No. of sampling sites in Lop Nur (Table 2)

Sub

surf

ace

sali

nity

(%

)

R Square=0.784Standard Deviation=2.03

-25

-20

-15

-10 Multiple scattering contribution (dB

)

Comparison of multiple scattering component of Cloude decomposition and salinity of subsurface medium, where R Square and standard deviation are also shown.

Polarimetric Analysis and Results

Retrieved Salinity of subsurface lacustrine deposits based on the Cloude decomposition.

It is found that subsurface salinity can well express the image feature of Lop Nur Lake shorelines, which indicates salinity making significant contribution to backscattering intensity on SAR image.

Polarimetric Analysis and Results

RADARSAT-1 image (1999) and TM image (1997)

Polarimetric Analysis and Results

Interpretation map of Lop Nur Lake and other targets based on SAR images

Conclusion

Based on analysis on physical and chemical properties of lacustrine deposits, the subsurface scattering structure of the Lop Nur was proposed in this report.

Physical scattering mechanism of bright and dark regions with different image texture in Lop Nur Lake was analyzed with polarimetric parameters including co-polarization correlation and degree of polarization.

Conclusion

There are three important scientific findings in this study.

The total area of the vanished Lop Nur Lake is more than 10,000 km2, much larger than 5350 km2 as reported.

The relatively younger West Lake is superposed on the top of the lacustrine deposits of East Lake, so the Lop Nur Lake actually has nearly circular, closed shorelines.

The drying-up process of East Lop Nur Lake went through 6 phases according to the shorelines interpreted from multiple SAR data.

Conclusion

Other polarimetric parameters, such as Shannon Entropy, can provide more information, and there needs certain physical explanation.

Future focus