QUANTITATIVE EVALUATION OF LANDSAT 7 ETM+ SLC-OFF IMAGES FOR

SURFACE VELOCITY ESTIMATION OF MOUNTAIN GLACIERS a

Yongling SUN 1,2); Liming JIANG 1); Lin LIU 1,2); Sisheng WANG 1,2); Gang Li 3）；Hansheng WANG 1)

1）State Key Laboratory of Geodesy and Earth‘s Dynamics, Institute of Geodesy and Geophysics, CAS，Wuhan 430077

2）University of Chinese Academy of Sciences，Beijing 100049

3）Institute of Space and Earth Information Science, The Chinese University of HongKong

Introduction & objectives The Landsat mission series (Landsat 1-5, 7 and 8) provide the only

detailed and consistent data source for mapping and monitoring the

global glacier changes over the last 40 years. However, the scan-line

corrector (SLC) of the ETM+ sensor on board Landsat-7 permanently

failed at 31 May 2003, which formed wedge-shaped data gaps from the

nadir path in any SLC-off images, resulting in roughly 22% of the pixels

to be missed. The SLC failure has left a serious problem for the glacial

applications of ETM+ data, particularly for monitoring long-term glacier

dynamics in High Asian Mountain where has few available data due to

the frequently cloudy covers.

In this study, we aim to evaluate the potential of the Landsat-7 SLC-off

images to derive surface velocities of mountain glaciers.

Study area

We select the

Siachen glacier as our

test site, which is

located in the central

Karakoram. At about

72km long, it is the

longest glacier in the

Karakoram and the

second largest valley

glacier in the world

outside the polar

region. Figure 1.

shows the study area

location. The black

solid line is the border

of the Siachen glacier.

The black dashed

(AA’) line is the center

line.

Results

Conclusions and perspectives

The work in this paper was supported by National Key Basic Research Program of China (973 Program, grant No. 2012CB957702), National Natural Science Foundation of China (Grant No.

41274024) and the Hundred Talents Program of the Chinese Academy of Sciences (Grant No.

Y205771077). The authors thanks NASA for providing the used Landsat TM/ETM+ imagery and SRTM DEM.

ESA – MOST China Dragon Cooperation, 2015 DRAGON SYMPOSIUM, 22 to 26 June 2015, Interlaken, Switzerland

Figure 3. Comparison of the glacier annual average surface velocity. (a)

Velocities estimated with Landsat TM images; (b), (c)Velocities estimated

with Landsat ETM + SLC-off images recovered by LLHM and WLR,

respectively; (d) Surface velocities along center line(AA’ in Figure 1).

Data and method

In the study, a pair of SLC-off images acquired on 12 Aug 2009 and 31

Aug 2010 were used for the purpose of evaluating the potential of the

Landsat-7 SLC-off images in deriving surface velocities of mountain

glaciers. Moreover, another pair of SLC-off images acquired on 27 Jul

2009 and 2 Oct 2010 were used to repair the above corresponding

images. Due to lack of the in situ measurements, we utilized glacier

velocity from two Landsat TM images acquired on 4 Aug 2009 and 23

Aug 2010 to verify the results of the recovered SLC-off images.

The main processing chain consists of three steps: (1) Two typical

filling-gap methods, the localized linear histogram match (LLHM)[1] and

the weighted liner regression (WLR)[2], were utilized to recover the

mentioned SLC-off images. (2) These two recovered pairs were

respectively applied for deriving glacier-surface velocities with the

COSI-Corr feature tracking procedure. (3) The resulting glacier

velocities were quantitatively compared with that of a pair of Landsat-5

TM images which were acquired nearly at the same time with the SLC-

off pair.

Figure 2. Comparison of a SLC-off

image before and after filling-gap. (a)

Landsat ETM+ SLC-off image

acquired on 12 Aug 2009; (b),(c) the

results recovered by LLHM and WLR,

respectively. The Landsat ETM+ SLC-

off image is recovered well by both

the LLHM and WLR methods. But the

WLR method achieves a better

performance of gap recovering than

the LLHM method.

◄Ice velocity

vector

References Acknowledgee

[1] USGS (2004).Phase2 gap-fill algorithm: SLC-off gap-filled products gap-fill algorithm methodology.

Available online at landsat.usgs.gov/documents/L7SLCGapFilledMethod.pdf

[2] Zeng, C., H. Shen and L. Zhang (2013). "Recovering missing pixels for Landsat ETM+ SLC-off imagery

using multi-temporal regression analysis and a regularization method." Remote Sensing of Environment

131: 182-194.

Email: jlm@whigg.ac.cn

A

A’

a

c

b

a

c

b

d

The recovered results show that the WLR method achieves a better

performance of gap recovering than the LLHM method.

The surface velocities estimated with the recovered SLC-off images are

highly agreement with those of the TM images, which demonstrates

that Landat ETM+ SLC-off data can be utilized to estimate the surface

velocities of mountain glaciers.

The annual mean velocity of the Siachen glacier is approximately 70

m/yr between 2009 and 2010 with a maximum of 280 m/yr close to the

glacial equilibrium line that are similar with the results in previous

studies.