In: Wagner W., Székely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B 
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ACTIVE AND PASSIVE MICROWAVE REMOTE SENSING OF SPRINGTIME NEAR 
SURFACE SOIL THAW EVENTS AT MIDDLE LATITUDES 
L. Han* 3 , A. Tsunekawa 3 , and M. Tsubo 3 
3 Arid Land Research Center, Tottori University, 1390 Hamasaka, Tottori 680-0001, Japan 
(han, tsunekawa, Tsubo)@alrc.tottori-u.ac.jp 
Technical Commission VII Symposium 2010 
KEY WORDS: Snow Ice; Soil; Application; Estimation; Algorithms; Radar; Passive 
ABSTRACT: 
Springtime near-surface soil thaw event is important for understanding the near-surface earth system. Previous researches based on 
both active and passive microwave remote sensing technologies have paid scant attention, especially at middle latitudes where the 
near-surface earth system has been changed substantially by climate change and human activities, and are characterized by more 
complex climate and land surface conditions than the permafrost areas. SSM/I brightness temperature and QuikSCAT Ku-band 
backscatter were applied in this study at a case study area of northern China and Mongolia in springtime of 2004. The soil freeze- 
thaw algorithm was employed for SSM/I data, and a random sampling technique was applied to determine the brightness temperature 
threshold for 37 GHz vertically polarized radiation: 258.2 and 260.1 K for the morning and evening satellite passes, respectively. A 
multi-step method was proposed for QuikSCAT Ku-band backscatter based on both field observed soil thaw events and the typical 
signature of radar backscatter time series when soil thaw event occurred. The method is mainly focuses on the estimated boundary of 
thaw events and detection of primary thaw date. The passive microwave remote sensing (SSM/I) based result had a good relationship 
with the near-surface soil temperature, while the active microwave remote sensing (QuikSCAT) based result had both relationships 
with temperature and soil moisture conditions. And also, QuikSCAT result identifies the geographical boundary of water-drove thaw 
event, which is crucial for understanding the different types of springtime near-surface soil thaw at middle latitudes. 
1. INTRODUCTION 
Near-surface soil freeze-thaw cycles have an important role in 
earth systems and directly affect the terrestrial hydrological 
cycle. Remote sensing provides an effective way for such event 
detection, especially, the microwave remote sensing (Zhang, et 
al., 2004). Microwave remote sensing based near-surface soil 
thaw event detection at mid-latitudes where near-surface 
changing seriously still rare (Han, et al., 2010). Generally, in 
active microwave remote sensing, the thaw event was detected 
based on the radar backscatter change which is responded to the 
dielectric constant of the surface; and in passive microwave 
remote sensing, the thaw event was detected based on the 
brightness temperature’s increasing. 
Scant attentions have paid in mid-latitude areas, which 
suggested our objectives as follows: 1) to detect and validate 
springtime soil thaw event by passive and active microwave 
remote sensing data; 2) to understand the difference in the 
results from active and passive microwave remote sensing data. 
2. STUDY AREA 
Our study area (Figure 1) lies between latitudes 31°N and 55°N 
and longitudes 71°E and 136°E including different humidity 
zones from arid to humid. 
Figure 1. Study area 
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