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Poster Session R
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Image processing of airborne shortwave infrared split-spectral scanning data in detecting oil pools by using Remote Sensing techniques
Li Jiahong, Zhang Jiangzhong, Yang Hong, Zhu Boqin
Institute of Remote Sensing Application, CAS
Abstract
Hydrocarbon content anomalies in soil above oil pools are a good direct indicating index on the earth surface. It was confirmed that the index possessed two absorption peaks at the wavelength 2.31mm and 2.35mm by spectral measurement in the laboratory and in the field. Oil Remote Sensing anomalies were obtained by airborne shortwave infrared split- spectral scanning images through computer image processing based on spectral features of the index.
These results was proved to be correspondent with the ascertained distribution of oil pools.
Introduction
N-12 oil field, located at the north-east of Xinjiang, had been chosen as the test-site (Fig. 1) to study the method of Remote Sensing image processing to oil exploration.
The test site is in the front edge of an alluvial fan, which developed at the north foot of Tianshan Mountains, in east of Junggar Basin. It is adjacent to Guerbantonggute Desert and the terrain is almost even. In most part of the area there develop[ed saline-alkali soil and covered sparse vegetation; In a few marshlands there grew some bog plants.
The test site is located at the north Bei-santai Palaeo-dome. A south-pitching fault named Beisantai fault spans the center of the area from the east to west. There developed two nose-like anticlines in the
north of the fault.
In this area it has been already exploited that the distribution and scale of the oil pool was coincided with two Permian nose anticlines and another U-like oil area in the south of Beisantai fault.
From the aforementioned analysis this test site was considered as a typical one for the theme.
Spectral Features of Hydrocarbon Materials and Analysis of ASISS Data
1. Analysis of Spectral Features of Hydrocarbon Materials
Ingredient of hydrocarbon materials in soil was approximate to that of crude oil. The obvious absorption valley at the wavelength of 2.27-2.47 mm was found by spectral measurement. There were two peaks at the wavelength of 2.31mm and 2.35mm which were caused by the overtone and combination tone vibrations of –CH and –CH (fig. 2).
The spectral features of crude oil and those soil samples above the oil pools in the laboratory and in the field were clearly stable and comparable.
It has been proved that there were hydrocarbon content anomalies in soil in test site and the band at the wavelength of 2.27 to 2.46mm was very useful. The spectral characteristics of the index was the theoretical bases to oil exploration by applying Remote Sensing techniques.
2. Analysis of ASISS Data
Airborne shortwave infrared split-spectral scanner is one of the best sensors to detect oil pools at present. Its work-band of 12 channels ranges from 1.5mm to 2.5mm. Eight channels were chosen in this experiment based on the analysis of spectral features. Parameters of the central wavelength, band width and detecting targets of each channel are described in Table 1.
The table revealed that channel 6 and 7 were two spectral characteristic ones to explore hydrocarbon content anomalies in soil.
Since the spectral overlap of the channels is high and so is the correlative coefficient among the channels data, the anomalies information as weakened. How to enhance, extract and distinguish the anomalies is one of the major problems to be solved in this paper.
Image Preprocessing of ASISS data
There excited radiant and geometrical deterioration and the distortion along scanning orientation in the test image whose size is 2-48 I * 256 c * 8 b. The image would not be correct unless it was preprocessed.
1. Image distortion along scanning direction and rectification
Ground resolution of each pixel is different along the scanning direction on an image. the one of the pixel properly under the airplane is maximum : 30m * 30m. It decreased while scanning visual angel increased.
According to the regular distribution pattern of resolution along the orientation, TANGENT transformation model was established and applied to finish the rectification of this distortion on test site images. Corrected image size was 2048| * 320 c
2. Radiative distortion and correction
We picked image of band 6 as a example to discuss the distortion (image – 1). It showed that the left side was dark was the right was bright; in accordance with DN profile distributive cure of the identical earth surface features on the image, we discovered thath DN value was low on the left and high on the right. In the light of analysis of DN histogram distribution of the whole image, we also found that its distribution was not normal. From these three aspects, it was confirmed that the original band 6 image was clearly distorted by radiant, so were the others.
The NORMAL method was used to redress the distortion. Its radical principle was summarized as follows :
Firstly, respecting average and mean square deviation for each band was designed. Secondly, image distortion curve was acquired by analyzing statistics results of the whole image; Thirdly, DN value of adjustment was calculated in column order. At last, pixel DN value of the whole image was resampled with the adjustment.
In the processing, we set the respecting means 128 and deviation 15 for all bands on the basis of balance analysis of statistics results for each band. We obtained radiant rectified images that wee comparable each other (Image -2 ).
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