Short- Term change detection with precise geometric correction and sub-pixel land cover characterization of modis
Kei Oyoshi,Wataru Takeuchi,Yoshifumi Yasuoka
Institute of Industrial Science, University of Tokyo
4-6-1 Komaba, Meguro, Tokyo 153- 8505
Tell: (81)- 3-5452-6417
Fax: (81) -3 5452-6414
E-mail: kooyoshi@iis.u- tokyo.ac.jp
Japan
Abstract
Earth observation satellite Terra was launched in 1999. High spatial resolution and high frequency
observation capability of Terra/MODIS ensures that every point on our world is observed every 1 – 2 days in
36 discrete spectral channels. MODIS is, therefore, expected to monitor short- term changes of earth’s
surface in more detail. This research develops sub-pixel scale image comparison algorithm for MODIS
250m data to detect small scale land cover changes. For sub-pixel scale image comparison, a spectral
mixture analysis was developed based on the linear mixture model. This algorithm made it possible to
compare the land- cover category mixing ratio within the same pixel in the two different date images and
detect the sub-pixel scale changes in land cover. Firstly, pattern matching was conducted to validate the
accuracy of geometric correction by WebMODIS system. The result shows the accuracy to be quite
satisfactory. Secondly, short- term land-cover change was examined by linear mixture model. But, the
differences of slope effect, atmospheric conditions and mis-registration caused a lot of noise errors. Finally,
by applying the filtering algorithm and setting threshold, mis-detection reduced effectively and short- time
land cover change was detected with quite high in pixel level.
Introduction
Land cover change is interface of environmental changes. Since land cover change induced by human
activities causes variation in temperature, atmosphere, or ecosystem and so on. It is important to monitor
land cover change. Remote sensing established itself to be the most effective tool to do that, as it can get
the surface information extensively, simultaneously, periodically and quickly. High spatial resolution and high
frequency observation capability of MODIS as earth observation satellite launched in 1999, ensures
observing the same area almost everyday with a spatial resolution of 250m in visible and near infrared
channels. Presently, there is no sensor to monitor short- term land cover changes as detailed as MODIS.
MODIS is expected to monitor short-term land cover changes, for example disasters, illegal dumping, rice
harvesting and so on, in more detail at the earth surface. For detecting small scale changes in urban areas
or complicated landscape areas from MODIS images, precise geometric correction is necessary to overlay
time series satellite images exactly and to identify the same areas in two images. Sub-pixel level
comparison of land-cover characteristics will be needed to detect changes in the pixel of 250m. In this case,
detecting small scale changes in urban areas or complicated landscape areas by using the different date
MODIS images, precise geometric correction is indispensable to overlay a pair of satellite images exactly
and to identify the same areas in two images. The objects of this research are to examine the accuracy of
geometric correction by pattern matching and to develop the algorithm for short-term land cover change
detections in sub -pixel level to detect change.
Modis Data used in this study
Institute of Industrial Science (IIS), University of Tokyo has been receiving and archiving MODIS data
since May 2001. IIS has started to process and distribute MODIS data through the web for the benefit of the
scientific community at WebMODIS, “http://webmodis.iis.u-tokyo.ac.jp/”, since Sep. 2002. This system
provides spatially subset data based on the request of end - users. We downloaded cloud-free MODIS data
acquired on 10 Mar. 2002 and 12 Mar. 2002. Both data has two channels with 250m spatial resolution.
Digital counts were converted to radiance followed by geometric correction. The study area in a 300 x
300km
area in the Kanto district of Japan, as shown in Fig.1. Fig.2. shows the MODIS image of the study
area for 10 Mar. 2002.
Fig 1. Kanto district in Japan
Fig 2. MODIS image (visible and near infrared channels) of study area. 10 Mar. 2002
