lab 1 introduction to envi
TRANSCRIPT
Lab 1
Introduction to ENVI
Remote sensing for agricultural applications: principles and methods (2013-2014)
Instructor: Prof. Tao Cheng ([email protected])
Nanjing Agricultural University
April 1st, 2014
Why ENVI?
• One of the best remote sensing software packages in the world
• Very popular in academic institutions
• Famous for hyperspectral analysis
• Developed using the programming language IDL and therefore easy to be extended with IDL
ENVI versions
Latest version: ENVI 5.1 + IDL 8.3
ENVI 5.1
• ENVI 5.1 Classic has the ENVI heritage interface. • If you are a long time ENVI user since ENVI 4.0, you may want to use the Classic one.
Run your old IDL scripts in ENVI Classic.
• A significant change in the interface • Changes in ENVI and IDL programming
ENVI • Start(开始) -> Programs(程序)-> ENVI 5.1 -> Tools -> ENVI Classic + IDL
• After ENVI Classic is started, you should see a menu as below:
• Interactive Displays
• File management
• Basic Tools
• Classification Tools
• Transform Tools
• Filter Tools
• Spectral Tools
• Map Tools
• Vector Tools
• Topographic Tools
• Radar Tools
Test data: a Landsat Scene
• Collected by the OLI on Landsat-8
• Time of acquisition: 2014-03-16, 05:07:50
• Data_type = “L1T” (Landsat-8 Level 1
Terrain corrected product)
• Satellite orbit location at acquisition:
path=119, row=238
• File type: each band is in a separate GeoTIFF
file
• Data format: 16-bit unsigned integer
• LANDSAT_SCENE_ID =
"LC81190382014075LGN00"
• Data download:
http://earthexplorer.usgs.gov/
• Data files
▫ 8 TIFF files and one txt file
• We only use the 7 multispectral bands.
A Landsat-8 false color composite (4-5-3)
Landsat 8 Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) Launched February 11, 2013
Bands Wavelength
(µm) Band center
(µm) Resolution
(m)
Band 1 - Coastal 0.43 - 0.45 0.433 30
Band 2 - Blue 0.45 - 0.51 0.482 30
Band 3 - Green 0.53 - 0.59 0.562 30
Band 4 - Red 0.64 - 0.67 0.655 30
Band 5 - Near Infrared (NIR)
0.85 - 0.88 0.865 30
Band 6 - SWIR 1 1.57 - 1.65 1.610 30
Band 7 - SWIR 2 2.11 - 2.29 2.200 30
Band 8 - Panchromatic 0.50 - 0.68 0.590 15
Band 9 - Cirrus 1.36 - 1.38 1.375 30
Band 10 - Thermal Infrared (TIRS) 1
10.60 - 11.19 10.800 100
Band 11 - Thermal Infrared (TIRS) 2
11.50 - 12.51 12.000 100
Landsat -8 band designations
What to do with this Landsat scene in
ENVI?
1. Image loading
2. Image displaying
3. Image stacking
4. Image cropping
5. Image calibration
• All the file and sensor types
that supported by ENVI 5.1
classic .
• These files can be directly
opened in ENVI.
• We are going to open
Landsat-8 image files that
are downloaded in GeoTIFF
format.
• Tips: to select multiple files,
hold the Ctrl key and click.
Load your data • Once your files are loaded into
ENVI, you should see this window (Available Bands List).
Display mode Gray Scale: individual bands RGB Color: band combinations (e.g. R-NIR-G) Try making different color composites
Data info: Dims 7791 x 7941: # of columns x # of rows Unsigned Int: data type = Unsigned integer (16 bit) (data range?) BSQ: data storage method What is the file size of a 7-band Landsat-8 image?
Interactive
displays Image window
Scroll window
Scroll window
Zoom control
1. Be familiar with the display group. Navigate on your image and focus on your target area.
Image window
Scroll window
Scroll window
Zoom control
2. Double click in the Image window to display cursor info.
How to read these values: Disp #: (col #, row #) Scrn: screen values (0~255) Projection: coordinate system Map: coordinates in m LL: coordinates in Lat/Lon Data: DN for the RGB bands
Image window
Scroll window
Scroll window
Zoom control
3. Right click in any window to bring up a box with commonly used functions.
Right click with your mouse:
How to locate the pixel for Ruigao (32.26598º N, 120.76102º E)?
Save data as ENVI
standard format
Load Landsat-8 bands 1~7 and stack them up to generate a multispectral image file.
Step 2
Step 1
Step 3
Step 4
Edit band
names
Assign meaningful band names.
Step 2
Step 1
Step 3
Step 4
• Find this file in your working directory.
• Check if the file size
matches the number you calculated in slide 8.
Image
cropping:
create a
subset image Step 1: draw a rectangle ROI in the Scroll window to include your study area (hold left key and drag, right click to select).
The subset image is in display.
Conversion of DN to TOA (Top
of Atmosphere) radiance
• 𝐿𝜆 = TOA spectral radiance (W/m2*srad*um)
• 𝑀𝐿 = the band-specific multiplicative factor (RADIANCE_MULT_BAND_x)
• 𝐴𝐿 = the band-specific multiplicative factor (RADIANCE_ADD_BAND_x)
• DN = Landsat-8 level-1 product pixel values
𝐿 = 𝑀𝐿 × 𝐷𝑁 + 𝐴𝐿
Step 1 Step 2
Input band-specific
gain and offset values
• Gain = RADIANCE_MULT_BAND_x (in the *_MTL.txt file) • Offset = RADIANCE_ADD_BAND_x
Compare DN data to radiance data
Radiance data Unit: W/m2*srad*um
DN data Unit: dimensionless
Resources
• ENVI help documentation • http://www.exelisvis.com/Company/PressRoom/Blogs/ImagerySp
eaks.aspx - Imagery Speaks Blog (a good blog site) • http://www.exelisvis.com/Learn/EventsTraining/Webinars.aspx -
ENVI/IDL webinars
• http://www.exelisvis.com/ProductsServices/IDL.aspx - Exelis VIS, the developer of IDL.
• http://www.exelisvis.com/Company/PressRoom/Blogs/IDLDataPoint.aspx - IDL data point (a good Blog site)
• LearnIDL.com – Dr. Ken Bowman’s web site • http://www.idlcoyote.com/ - Coyote’s guide to IDL programming
(IDL tips, training, consulting) • http://gumley.com/ - Practical IDL programming (IDL book) • http://michaelgalloy.com/ - resources for IDL developers
Class project
• Think about what to do in your project.
• Make a tem of two students for each project.
• Start developing ideas and collecting materials (making notes is necessary) for your project.
• Allocate reasonable workload.