Remote Sensing Lab Assignment
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Transcript of Remote Sensing Lab Assignment
IN 84.21 Remote Sensing and GIS for Disaster Mitigation – Laboratory
Lab Excercise Report #1
Introduction of Basic Tool and Color Composition Images
By: Wifandy RT Purba Sidadolog
#114354
Disaster Preparedness, Mitigation and Management (DPMM) Asian Institute of Technology ‐ AIT
2012
Laboratory Exercise 1 INTRODUCTION OF BASIC TOOL AND COLOR COMPOSITION IMAGES
Date : August 28, 2012 Students Name : Wifandy Raymond Tobias Purba Sidadolog ID : 114354 Lab Instructor : Dr. Sarawut Ninsawat and Mr. Chudech Losiri INTRODUCTION Remote Sensing is the science and art of obtaining information about an object , area, or phenomenon through the analysis of data acquired by a device that is not in contact with the object, area, or phenomenon under investigation[1]. In relation with a disaster cccurence, the technology of Remote Sensing is widely used, if not said, a very significant aspect during the process of preparedness, mitigation and response of the disaster [2]. In relation with disaster management, the earth observation through satellite plays a significant role. Geospatial data sensed through space technology (satellite) has been widely used during the disaster management process for i.e.:
‐ Monitoring of natural hazards potential for natural disaster occurence (i.e. flood) ‐ Rapid Assessment of disaster impact ‐ Locating places for refugees ‐ Decission making for infrastructure repair priorities ‐ And so on.
However, to deliver its purpose, the geospatial data received from satellites need to be processed through certain computer technology by a competent person, before it can be used easily by decision makers. ERDAS IMAGINE 9.3 is is a remote sensing application with raster graphics editor abilities designed by ERDAS for geospatial applications. This software allows the user to prepare, display, and enhance digital images. By manipulating the raw data using this software, it is possible to analyze some objects which are normally not visible [3]. OBJECTIVES This Lab Session is intended to make students familiar with this ERDAS 9.3 Image Processing Software and with the multispectral data. The image processing is used to process the image for the purpose of Disaster Management (Preparedness, Mitigation, and Response). Student will open and manipulate individual band of Landsat TM data using ERDAS IMAGINE. DATA TO BE USED The image used during this lab is LANDSAT 5 TM Image. The TM Image always covers a 185 x 185 km area [4]. The LANDSAT 5 TM Image was stored in the AIT network address: //ibmserv/public_dellserv/ Landsat 5 is a Sun Synchronous Satelite launched on March 1, 1984 equipped with two multispectral sensors: a Multispectral Scanner (MSS – 4 spectral bands) and a Thematic Mapper (TM – 7 spectral bands). The characteristic of Landsat 5 is: Orbit Type : Sun‐synchronous Polar. Altitude : 705 km Orbit Period : 98.9 min Total FOV : 14.920 (185 x 185 km)
Inclination : 98.20 Repeat cycle : 16 days (233 revolutions) Equatorial crossing time : 10.00 AM The TM Sensor 7 Spectral Band characteristics[2],[5].
Band Spectral Band (µm)
Resolution Use
1 – Blue 0.45 – 0.52 30 x 30 m Ground/plants differentiation, coastal zones, Bathymetric mapping, distinguishing soil from vegetation and deciduous from coniferous vegetation
2 – Green 0.52 – 0.60 30 x 30 m Vegetation: Emphasizes peak vegetation, which is useful for assessing plant vigor
3 – Red 0.63 – 0.69 30 x 30 m Plant species differentiation, discriminates vegetation slopes
4 – Near IR 0.76 – 0.90 30 x 30 m Emphasizes biomass content and shorelines
5 – Shortwave IR 1.55 – 1.75 30 x 30 m Snow/cloud differentiation, Discriminates moisture content of soil and vegetation; penetrates thin clouds
6 – Thermal IR 10.4 – 12.5 120 x 120 m Thermal mapping and estimated soil moisture
7 – Shortwave IR 2.08 – 2.35 30 x 30 m Hydrothermally altered rocks associated with mineral deposits
METHODOLOGY In this Lab session, students are particularly assigned to achieve two goals of skill set: 1. Display Satellite Image in Color Composite of True Color, False Color, Pseudo Color, Gray scale and Relief[5]
A color composite is the color of image generated by composing three selected multi‐band images with the use of three primary color (RGB). The RGB indicates three different objects. We can display images in different colors, depending by the selection of three band images asigned to the three primary colors. The true color composite is when three filters of R, G and B are assigned to the same spectral regions of red (Band 3), green (Band 2) and blue (Band 1), almost the same color as the natural scale. The reproduced image is called a True color or natural color composite. While the False color composition is when the visible regions (1, 2, 3) or other invisible regions (such as IR Bands) are assigned/allocated to RGB Filters For displaying images with different Band combination assigned to the RGB filters we use Tools from View Tab. The steps are ‐ Open a file and choose the original image (Landsat5.img) ‐ Use the Raster tab, choose display as True Color. ‐ Change Band combination and assign to RGB. For True Color Composite, Red is assigned with Band 3,
Green with Band 2, and Blue with Band 1. For False Color Composite, we are trying several combination to see the results
Pseudo color image is displayed when difference of colors are assigned to the subdivided grey scale of a single image. For displaying a pseudocolor image, we use tools from View Tab. The steps are
‐ Open a file and choose the original image (Landsat5.img) ‐ Use the Raster tab, choose display as Pseudocolor with Layer 6 (Thermal IR) ‐ On the Viewer window choose Raster, then select Attributes, Edit, than Colors ‐ Change Colors to see different combinations. For displaying a Gray scale image, we use tools from View Tab. The steps are ‐ Open a file and choose the original image (Landsat5.img) ‐ Use the Raster tab, choose display as Grey scale with Layer 4 (Near IR) For displaying a Relief image, we use tools from View Tab. The steps are ‐ Open a file and choose the original image (Landsat5.img) ‐ Use the Raster tab, choose display as Relief with Layer 4 (Near IR)
2. Create Subsection a data set [5]
Subsetting an image is a process to delimit a small area of interest from the input image that covers larger area than necessary. For creating a subset data, we use tools from Data Preparation Tab. The steps are: ‐ Select Subset Image ‐ Choose Input File “Landsat5.img” and create a output file name in a selected folder ‐ Specify the coordinates of all for edges of our area of interest. In this Lab session the coordinates are as
follows: ULX : 659995 ULY : 1565845 LRX : 693832 LRY : 1542288
‐ Click ok. RESULT AND DISCUSSION Below are the screenshots of the output images during the Laboratory Excercise on August 28, 2012. There are several combination excercised during the Lab session (more than 20 combinations), which some of the screenshots are represented below (not all combination’s screenshots are displayed in this report).
a. Output of True Color Composite (3, 2, 1 Bands assigned to the R‐G‐B Filters). This is the combination of Band 3, 2 and 1 assigned to the RGB Filter. With this image we can easily identify the River (Blue‐Greenish), Buildings (White rectangulars), vegetations (Green Gradations), and Barelands (Brownish). The different greens (gradation) can be interpreted as different kind or different condition of the vegetations.
b. Output of False Color Composite (several combinations of Band assigned to the RGB Filters) 4‐3‐2 Band Combination 5‐3‐2 Band Combination
7‐2‐1 Band Combination 6‐4‐5 Band Combination
2‐5‐3 Band Combinations 7‐5‐4 Band Combinations
By selecting different of Band Combination, we can identify the different objects which are in different color grade. However, except the river stream which shape is very unique, it is difficult to interprete the other objects and meaning of the colors.
c. Output of Pseudo Color Image Pseudo Color Image of Layer 6 (Thermal IR) in Cyan‐to‐Red Gradation
The use of pseudocolor is especially useful for displaying data that are not reflection measures, for example the Thermal infrared red data. By displaying this Pseudocolor Image of Layer 6 (Thermal IR) we can see the the association of cold‐warm with red‐yellow data, which is more intuitive [6].
d. Output of Gray Color Image and Relief Image Gray Scale Image Output Relief Image Output
From both image output, we can identify the boundary and shape of the objects, however, except the river stream which shape is very unique, it is difficult to interprete and conclude the actual form of the object, whether it is a building, a farm, a fields, or barelands.
e. Output of Subsetting the image
Subset image (wifandy.img ‐ A) compared with source image (Landsat5.img ‐ B) in True Color Composition.
By inputting the coordinate of the edges/corner in the subset parameter, we can create a subset image covering our area of interest and discard other part of the image.
A B
CONCLUSION We can display the satellite image from Landsat 5 Thematic Mapper (Landsat 5.img) in several ways, using the Raster Options (True Color Image, False Color Image, Pseudo Color Image, Gray Color Image, and Relief Image). This option is very important in the concept of data visualization and contrast enhancement, as it gives us the ability to choose the best combination of TM Spectral Bands assigned to the R‐G‐B filter. By having the knowledge of the Landsat 5 TM Bands characteristic, we can analyze the output images and interprete the objects. The selection of Bands assigned to the RGB Filters, depends on the purpose of image analysis. For Land Surface Observation Analysis, the combination I like the most is the True Color Composition 3‐2‐1. Using this True Color Composition, we can interprete the buildings, the river stream and the vegetation as their real color. The different gradation Green‐Blue of the water body and the different gradation of the Green vegetation represents some divergent condition of the water body and vegetations. Also the Brownish area represents the bareland. This kind of Image is widely used in Disaster Management such as on disaster prone area monitoring, rapid damage assesments, flood spread analysis, etc. This image output accesibility is also critical during the decission making process of Public Authorities related with disaster. By performing Image Subsetting on the original image, we can have a smaller/delimited area of interest, without loosing its resolution and band properties. It is important to select the accurate area of interest, to be more focus when working with the image. REFERENCES [1] Lillesand, T. M., Kiefer, R. W., and Chipman, J. W. Remote Sensing and Image Interpretations, fith ed. John Wiley & Sons, New York, NY, 2004 [2] Nirupama, Simonovic, S. P., Role of Remote Sensing in Disaster Management, Paper Series No. 21, ICLR Research, 2004. [3] http://en.wikipedia.org/wiki/Erdas_Imagine [4] http://eoedu.belspo.be/en/satellites/landsat.htm [5] IN 84.21 Remote Sensing and GIS for Disaster Mitigation Lab Manual provided by the Faculty [6] Kerle, N., Janssen, L. F., Hurneeman, G. H., Principles of Remote Sensing, 3rd ed. ITC, Enshede, The Netherlands, 2004