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FORMOSAT IMAGERY BARRAX (SPAIN)
PRELIMINARY ANALYSIS
Alfonso Calera, Isidro Campos, Jose Gonzalez-PiquerasInstituto de Desarrollo Regional. AlbaceteUniversidad de Castilla La Mancha (Spain)
Tolouse, January, 12th 2010
Objectives
Cross-comparison FORMOSAT_Landsat5-TM (on synchronous images 19/October/2009)
Preliminary assessment about crop multitemporal monitoring Materials:
Formosat imagery, processed by CESBIO (Olivier Hagolle) Orthorectificaction, Top of Atmosphere and Surface reflectances
Landsat imagery, processed by IDR-UCLM Orthorectification, ToA and Surface reflectances Formosat 2009/09/21 2009/10/03 2009/10/11 2009/10/19 2009/10/27 2009/11/05
Landsat 2009/09/10 2009/10/03 2009/10/12 2009/10/19299/10/28 (clouds)
Cross-comparison FORMOSAT vs. Landsat5-TM synchronous images 19/October/2009
The comparison has been performed for:
Reflectances_ToA Formosat-Landsat5-TM
Reflectances_BoA Formosat-Landsat5-TM
NDVI_ToA Formosat-Landsat5-TM
NDVI_BoA Formosat-Landsat5-TM
Besides, we analyzed the performance of the applied atmospheric correction, by comparison
Refl_BoA vs. Refl_ToA Formosat
Refl_BoA vs. Refl_ToA Landsat
METHODOLOGY for the comparison:
We set a grid over the study zone, i.e. full Formosat image, where each cell defines the surface to perform the aggregation from each sensor.g The side length of each grid cell determines the number
of individual pixels to be aggregated.g We select a length of cell size of the 90 m (3x3 pixel
Landsat). By this way we can avoid the different pixel size and the uncertainty in geolocation
g The comparison between observations from both sensors will be showed using the graphic representation and calculating the linear curve fit
Landsat 5 TM October 19 th 2009
Methodology for the comparison between reflectance and NDVI.
n cellFormosat
NDVI
IVDN
n
1KK
Formosat October 19 th 2009
)(
)(
RNIR
RNIR
kNDVI
n cell 5Landsat
NDVI
IVDN
n
1KK
Comparison reflectance,NDVI,…
Individual pixel reflectance and NDVI values :
Grid 90 m x 90 mPixel size: 8 m and 30 m
Where n is the number of pixels inside of the cell;
RGB 142 Formosat October 19 th 2009. Grid 90 m x 90 m
Landsat ...
Reflectance,
Mean NDVI, in each cell:
n is 90 x 90
n
NDVI
IVDN
n
KK
1
To increase the accuracy of calculation we split the original pixel size to other with 1 m length side
RGB 543 Landsat 5 TM October 19 th 2009. Grid 90 m x 90 m
Landsat ...
n is 90 x 90 for each cell
n
NDVI
IVDN
n
KK
1
To increase the accuracy of calculation, we split the original pixel to other with 1 m length side
RESULTS: Reflectances_ToA Formosat-Landsat5-TM
RESULTS: Reflectances_ToA Formosat-Landsat5-TM
A good linear fit is showed, but the scatter could be due to the remaining uncertainty of geolocation and to the differences on angle of view and illumination.Deviation from 1:1 line could be due to differences on the spectral band width and on the sensor function response
RESULTS: Reflectances_BoA Formosat-Landsat5-TM
RESULTS: NDVI_ToA Formosat-Landsat5-TM
NDVI matches 1:1 line and R2 is better than reflectances
RESULTS: NDVI_BoA Formosat-Landsat5-TM
RESULTS: About atmospheric correction applied
Refl_BoA vs. Refl_ToA Formosat
Atmospheric correction is equivalent to a linear transformation. No scatter is introduced by the applied atmospheric correction
RESULTS: About atmospheric correction applied
NDVI_BoA vs. NDVI_ToA Formosat
Scatter seems to be introduced by the non-linear characteristic of NDVI definition
RESULTS: About atmospheric correction applied
Refl_BoA vs. Refl_ToA Landsat5-TM
RESULTS: About atmospheric correction applied
NDVI_BoA vs. NDVI_ToA Landsat5-TM
Preliminary assessment about crop multitemporal monitoring
To visualize the temporal evolution we upload in the SPIDER system the RGB341 and NDVI from FORMOSAT and RGB543 and NDVI from Landsat .
Set the URL of SPIDER: http://161.67.130.130/spider/
Is under construction http://161.67.130.130/spider/
http://161.67.130.130/spider/fixedviewer/index.php
Maize, after a spring crop
Maize.
Maize.
Maize.
Maize:Discrepancies between NDVI values from F and L sensors, for one point, is dependent not only from the sensor, but also of the status of cover, BRDF?. Other effects about the spatial resolution could be avoided by the uniformity of cover in the case here showed.
Maize.
Maize.
Alfalfa.
In this case differences between sensors are little, in despite of high variability on the crop uniformity.
This is only a starting point ….
We need to perform further analysis for other dates under different conditions .....
Formosat time series could be a powerful tool to monitor crop development along its growing season.
Spatial resolution of Formosat imagery provides a great capability to monitor and visualize the uniformity of crops.