Category Archives: Remote Sensing & GIS
Applying mathematical operation on satellite image is an important processing step in remote sensing project. Lots of software such as MATLAB, ENVI, ERDAS and PCI Geomatica enable users to carry out these operation . However, the user interface and how to implement the operation into the software make them different with one another. Some software required basic knowledge of programming while other give more user-friendly and easier interface for the beginner. Above all software, one of the easiest software to perform simple mathematical operation on satellite images is by using ENVI.
In ENVI, the tools is called band math. (Basic Tool>Band Math)
Band math in ENVI enable user to perform basic mathematical operation, trigonometric function and other option such as Boorlean and relational operators. Today, i like to share about the list of mathematical band math operation in ENVI.
- Addition (+)
- Subtraction – (-)
- Multiplication – (*)
- Division – (/)
- Minimum operator – (<)
- Maximum operator – (>)
- Absolute value – (abs(x))
- Square root – (sqrt(x))
- Exponent – (^)
- Natural exponent – (exp(x))
- Natural logarithm – (alog(x))
- Base 10 logarithm – (alog10(x))
- Sine – (sin(x))
- Cosine – (cos(x))
- Tangent – (tan(x))
- Inverse sine/ Arcsine – (asin(x))
- Inverse cosine/ Arccosine – (acos(x))
- Inverse tangent/ Arctangent – (atan(x))
- Hyperbolic sine – (sinh(x))
- Hyperbolic cosine – (cosh(x))
- Hyperbolic tangent – (tanh(x))
There are still few more functions, however the list above is the most used ones in ENVI. Thanks you and don’t forget to bookmark us (Ctrl + D).
Lidar is the an acronym to light detection and ranging. Lidar uses billions of reflected light beams to map the topography. In Malaysia, Lidar is already been used for many applications mainly in transportation, disaster management, hydrology and telecommunications utilities. Lidar airborne survey is more preferable that other conventional method because it is faster, accurate (can reach 0.2m spatial resolution), and economical when large areas need to be covered.There are fews noticeable Malaysia remote sensing companies that doing Lidar airborne survey, which are:
1. AAM Group
2. Airborne Informatics Sdn Bhd
3. Ground Data Solutions Sdn Bhd
Feel free to drop your comment here if you know other lidar company that operate in Malaysia.
How to process lidar data
Free software to process lidar data
Point cloud processing software
VRMesh is an advanced 3D point cloud and mesh processing software tool.
It works as a plugin for microstaton and is suitable for both TLS and airborne lidar.
3. GRASS GIS
Has some good modules for processing and handling LiDAR data.
” a collection of highly-efficient, scriptable tools with multi-core batching that process LAS, compressed LAZ, Terrasolid BIN, ESRI Shapefiles, and ASCII.”
5. FME Desktop
” ability to take a point cloud that has no color information on it, and overlay it into an orthophoto to produce a colorized point cloud”
Add-on to ArcGIS
a powerful and solid open source option developed by the USDA Forest Service to analyze and visualize LiDAR data.
identifying tree canopy and creating DSM’s from Lidar data
During this week, news reported that forest fires happen at Sumatra, Indonesia which cause dangerous haze (API more than 300) at Singapore and some part of Johor, Malaysia.
By using remote sensing (RS) satellites, important atmospheric and land parameters such as LST (land surface temperature), wind direction, and aerosol optical thickness / air pollution index (API) can be retrieved to determine:
1. Location of forest fires
2. Direction of smoke
3. The hazardous level of haze .
Location of forest fires. (Source)
Near real time/ real time data of global forest fires are freely available at:
Image above retrieved on 20 June 2013 22:35 GMT show many hot spots at Sumatra, Indonesia (yellow box). This image produced using NASA EOS MODIS satellite.
Hazardous level of haze
Real time air pollution index (API) is freely available at http://aqicn.org/?map .
Different countries using different scale on how to describe the risky level of API. For Malaysia, the scale is given by:
From the image of API above (retrieved on 21 June 2013), Muar and Pasir Gudang are both within Johor reported more than 300 API (Very unhealthy). According to news report, Malaysia government already closed down schools at the haze affected areas. By history, the highest API value ever recorded was 839 in Kuching on 23 September 1997 during the 1997 Southeast Asian Haze.
As a remote sensing practisioner, once should know the main difference between orthorectification and rectification process.
Airborne / satellite Image Rectification involve the process of correcting the x and y coordinate of the distorted image. It does not consider the terrain relief displacement of the image. Common technique that can be used are by using ground control point, map-to-image rectification, and image-to-image rectification.
For orthorectification, it involve the process of correcting the x, y, and z coordinate of the distorted image. It will consider the terrain relief displacement. Generally, digital elevation model (Dem) is used as the reference to correct the image. However, ground control point that has height information ( x, y, z) can also be used.
That it for today. I try my best to share as much knowledge as i know. And do correct me if i am wrong. Thanks you.
What i plan to post in this blog
– remote sensing basic image processing tutorial such as : geometric correction, atmospheric correction, classification, mosaicking, and digitizing
– effective project presentation technique (how to make your slide presentation look great and attractive). I plan to write a short tutorial on how to create map layer using photoshop.
– creating 3d satellite image using arc scene and surfer 3d
And many more…
I believed that working in oil and gas industry is everyone dream especially for fresh graduates. According to “Top ten highest paying careers in engineering”, Petroleum engineer is the no.1 career that offer the highest payment followed by architecture and nuclear engineer. Besides, geoscientist which is the nearest career related to Remote Sensing and Geoinformation (GIS) is the no.9 top paying jobs in computers, mathematics and science industry. If we deeply look into the details of the industry background, oil and gas is one of the top high paying job internationally (including Malaysia).
So, here I list down some of the oil and gas company in Malaysia that hired remote sensing and GIS graduates.
3. you know more? please write a comment here.
Hi all, this week i got lots of assignment to be done. I think it is better for me to make a simple yet informative post. Specially posted to those who are searching internship or job vacancy in remote sensing fields in Malaysia. By the ways, most of the company also hired GIS (Geoinformation) background students. Enjoys!
1. Imatera Digital Image Service Sdn Bhd
2. Geomatika Technology Sdn Bhd
3. Innovative Mapping Solution
4. Geoinfo Services Sdn Bhd
5. RS & GIS Consultancy Sdn Bhd
6. IR Technic Sdb Bhd
7. Geosense Sdn Bhd
8. ANR Research Sdn Bhd
9. Myspatial Sdn Bhd
10. Echo Broadband Sdb Bhd
11. JP Survey Head Quarters
12. Atama Tech Sdn Bhd
14. Sky-shine Corporation
15. Aeroscan Precision (M) Sdn Bhd
16. ESRI Malaysia
17. Ground Data Solutions R&D Sdn Bhd
18. Airborne Informatics Sdn Bhd
19. AAM Group
If you know company that is not list down here, feel free to drop a comment so that i can update the list. Thanks you = )