Estimating Crop ET from SatelliteSection 2. Calculate ET from Satellite Data-V1

Outline• Calculate dT at hot and cold spots

Choose area of interest Locate a cold spot and find the surface temperatureLocate a hot spot and find the surface temperatureFind the local weather dataCalculate dT

• Calculate ETObtain daily Etr

Download the file “CalculateEt.xls”

Calculate the following

NDVI (Normalized vegetation index)

Ln(Zom) (the natural logarithm of roughness length)

H (soil heat flux)

Albedo (ground reflectance)

ET

Step 2Drag mouse to choose an interested area

Step 3Put mouse at the upper-left corner of the chosen area to

obtain coordinates

Step 4Put mouse at the bottom-right corner of the chosen area to

obtain coordinates

The green circled areas are pecan orchard and alfalfa field

Step 5Adjust the coordinates

Upper-left corner (from step 3)

4104/6=684 do not need to be adjusted

821/6=136.8 adjusted to 137*6=822

Bottom-right corner (from step 4)

4315/6=719.1 adjusted to 719*6-1=4313

993/6=165.5 adjusted to 166*6-1=995

Choose area of interest

step1Open the “Image3N” image in the file of

“AST_L1B_003_09042002175822_01142003061252.hdf”

Step 6Show the interested area only

Step 7Press the “Magnifier” to magnify the image to

find the Salopek pecan orchard

Step 8 put the mouse in the the orchard to find the coordinates

Using the same way to find a point coordinates in the alfalfa field for future locating NDVI

(slide 53)

Step 9 open “Kinetic Temperature” in “AST_08_003090420021758220000000.hdf”

Step 10 choose the interested area of upper-left (684, 137) and bottom-right (718,165) (see step 5)

Step 11 find the point coordinates in pecan orchard

According to step 8 and the point coordinates in the pecan field are (24, 18) in the “ImageData3N” chosen area, and

according to step 10, the starting coordinates of the upper-left coordinates in the chosen temperature image are (684, 137).

So the point coordinates are684+24 /6~688137+18/6~140

Step 12 find the pecan orchard temperature (688, 140) in the chosen area spreadsheet.

Locate a bare soil field and find its temperatureStep 1 open the chosen surface area as an image

Step 2 magnify the image by click on “Magnifier”

Step 3 find the hottest point (assume it is a bare soil field)

Find the local weather dataStep 1 go to:http://weather.nmsu.edu/cgi-shl/cns/stninfo.pl?stn=95

Step 2 Scroll down and click on “2002” in “Old hourly data”

Step 3 The hourly data in 2002 is shown. Please record which columns are “Humidity Mean”, “Wind Speed Mean”, and “Solar Radiation Mean”

Step 4 Scroll down and find the data at 12:00, 09/04/02

Step 5 Scroll to right and find the needed data “Humidity Mean=28.19%”, “Wind Speed Mean=5.4 mph”, and “Solar Radiation Mean=28.86 L/h”

using the recorded column positions in step 3.

Calculate dTStep 1

Download the Excel “DTSep0420021200.xls” file at:

http://weather.nmsu.edu/teaching_Material/soil470/sebal/Etcalculation/DTSep0420021200.xls

Step 2

Open “DTSep0420021200.xls” and input the obtained data.

The worksheet of “ETr calculation” worksheet calculates hourly Etr

The “Bare soil spot” worksheet calculates hot spot dT

The “dT graph” worksheet shows the linear equation for dT calculation

Calculate ETObtain Daily Etr

Step 1 Go to

http://weather.nmsu.edu/cgi-shl/cns/oldformat.pl

Step 2 fill out the date, choose “Metric (Excel)”, then fill in “ID” finally press “Retrieve Weather Data”

Then the Etr (PET) is calculated.

Download “CalculateEt.xls” Step 1

In Internet Explorer fill in the following URLhttp://weather.nmsu.edu/teaching_Material/soil470/sebal/ETCalculation/calculateEt.xls Then click “Yes”

Step 2 click No

Step 3 Click on “File“ then“Save As”

Step 4 Click on “File“ then“Save As” and give a file name and then “Save”

Calculate NDVIStep 1 close the Internet Explorer so that

the Excel software can open the dowloaded file.

Step 2 open Excel software and click “File” then “Open”

Step 3 choose the file and click “Open”

Step 4 click “Enable Macros”

Step 5 click “No” if the following dialog appears

Step 6 fill in the input values

Step 7 go to the opened “AST_L1B…” HDF file and copy the chosen area “ImageData3N” data.

upper-left (4104, 822) and bottom-right (4313, 995). See slide 9

Step 8 go to “Band3” Excel worksheet and paste the copied data

Step 9 using the same way copy the HDF “ImageData 2” data to “Band2” worksheet.

upper-left (4104, 822) and bottom-right (4313, 995).

The “NDVI 15by 15” worksheet automatically

calculates the NDVI in 15 by 15 m resolution

Step 10 click “Tools”, “Macro”, “Visual Basic Editor”

Step 11 click “Windows”, then “Module 1”

Step 12 click the “run” button to calculate the 90 by 90 m NDVI

Within 1 minute, the calculation finished and the results are in

“NDVI 90 by 90”

Calculate Ln(Zom)Step 1 find point (24, 21) in “NDVI 90 By90” and

obtain the NDVI for bare soil according to coordinates (23, 20) from slide 19

Step 2 find point (24/6+1, 18/3+1) in “NDVI 90 By90” and obtain the NDVI for pecan according to

coordinates (24,18) from slide 11

Step 3 find the point (120/6+1, 131/6+1), i.e. (21, 22) and obtain NDVI for alfalfa

according to slide 12 coordinates (120,131)

Step 4 input the NDVIs and pecan alfalfa heights and

bare soil roughness length in “NDVI LNZom” to obtain the regression equation for Ln(Zom)

Step 5 in “LnZom”, calculate Ln(zom) for each point using the regression equation

Calculate HStep 1 copy the chosen surface temperature data

from HDF file (slide 14) to the Excel “temperature “

The “Iteration” worksheet will automatically do iterative H calculation considering stability effects

until most H’s change within 10%

Albedo calculationstep 1 open the reflectance file

” AST_07_003090420021758220030000.hdf1”Must choose “All Files” on the dialog, otherwise, the file will not be

shown.

The opened file

Step 2 choose data area, the upper left coordinates are (2052, 411) and bottom-right (2156, 497)

Step 3 copy chosen area Band 9 data from HDF file to “Reflectance 9” of Excel file.

Step 4 using the same way copy the reflectance data of band 5, 6, 8 to the Excel worksheets of

“Reflectance 5, 6, 8” respectively

The part of albedo calculation for band 5, 6, 8, and 9 in the albedo regression equation will

be automatically calculated in “Reflectance 5 6 8 9 30by30m”

Step 5 Open the reflectance file of AST_07_003090420021758220030000.hdf0

Step 6 Copy the “Band3N” and “Band2” reflectance data from HDF file to Excel worksheets of “Reflectance 3n” and “Reflectance 1”. The upper-left coordinates are (4104, 822)

and bottom-right (4313, 995)

The part of albedo calculation for band 1, and 3 in the albedo regression equation will be

automatically calculated in “Reflectance 1 3 15by 15m”

Step 7 Open Visual Basic Editor to run the modules to convert the resulted 30 by 30 m and 15 by 15 m

albedo calculation to 90 by 90 m

Step 8 click “Tools”, then “Macros”

Step 9 click “Reflectance13Band15to90m” and then “Run” to covert 15 m by 15 m results to 90 by 90 m

Step 10 click “Reflectance5689Band30to90m” and then “Run” to covert 30 m by 30 m results to 90 by

90 m

The results for band 5, 6, 8, and 9 in 90 by 90 m resolution are in the worksheet of “Reflectance 5 6 8

9 90by90m”

The results for band 1 and 3 are in the worksheet of “Reflectance 1 3 90by90m”

The final albedo is automatically calculated and is in “Albedo” worksheet.

ET calculation and visualizationStep 1The net radiation is automatically calculated

in “Radiation net”

The regression equation for G/Rn is obtained in “G Div regression”

Step 2 The G/Rn is calculated in “G Div Rn” G is soil heat flux and Rn is the net radiationusing the regression equation from last slide.

Step 3 Rn-G is obtained in the worksheet of “Rn-G”

Step 4 Et is calculated in “ET”

Step 5 Scroll down and then the Et is calculated in “mm/day”

Step 6 Scroll down, and then the Et is rounded to integer because to visualize it in HDFView2.1, the format must be

integer.

Step 7 The ET results are visualized in HDFView2.1