Atmospheric Correction and Calculation of some physical indices of VNREDSat- 1A’s images 1 Supervisor: Student: Prof. Ph ạ m Văn C ự Ph ạ m Th ị Thanh Hoa Department of Geography, Hanoi University of Science Intake 2014-2016 Vietnam National University. Academic year: M1 334 Nguyen Trai Street, Hanoi City, Vietnam. Internship Report - PHAM Thi Thanh Hoa
Outline 2 1. Principle of Radiometric Correction 1.1. Conversion of Raw Image to Spectral Radiance Images. 1.2. Correction of Spectral Radiance to the Reflectance at the TOA and to the Surface Reflectance. 2. Calculation of Some Physical Indices of VNREDSat-1A Images 3. Preprocessing Methodology 4. Conclusion Internship Report - PHAM Thi Thanh Hoa
1. Principle of Radiometric Correction 3 L = L s + L p Where: L: The value of digital number (DN) of a signal L L s : Direct reflect Radiance of object L p : “Noise” Signal. Radiometric correction of satellite images is about to remove the “Noise” signal L p . By considering the surface of object is Lambertian surface (smooth and insignificantly different in elevation), the process will be done by following steps: - Radiometric correction at the receiver of the satellite. - Atmospheric correction Internship Report - PHAM Thi Thanh Hoa
1. Principle of Radiometric Correction 4 Four levels of images are: (1) Raw Image including digital number of pixels of objects. (2) Result of radiometric correction of receiver: converting images from DN (after receiver) spectral radiance L (before receiver) (which is presented as R on the Figure 2). (3) Result of converting R images to the reflectance at top of the atmosphere ρ TOA . (4) Result of converting images of reflectance at top of atmosphere to the surface. Internship Report - PHAM Thi Thanh Hoa
1.1. Conversion of Raw Images to 5 Spectral Radiance Images - Formula for VNREDSat-1A Correction: R ≡ Lλ = (DN / GAIN) + Bias (1) Where Gain and Bias is linearly changing parameters of the receiver after being accredited. For VNREDSat – 1A, Bias = 0. Processing Steps: Internship Report - PHAM Thi Thanh Hoa
1.1. Conversion of Raw Images to 6 Spectral Radiance Images Practical case for Hue: Parameters VNREDSat-1A (2013) Image Code Number V130514_034239 Acquisition Date 14/05/2013 Processing Level 1A Incident angle: 20.34 Satellite Angle (Degree) Azimuth: 358.93 Azimuth: 80.98 Solar Angle (Degree) Sun elevation: 74.8 Multi-Spectral Band Spectral Order XS1 XS2 XS3 NIR VNREDSat-1 (2013) Absolute 1.63825 1.62130 1.84789 2.51121 Gain Value (W/m 2 /sr/µm) Internship Report - PHAM Thi Thanh Hoa Spatial Resolution (m) 10 10 10 10
1.1. Conversion of Raw Images to 7 Spectral Radiance Images Practical Case for Hue: Composite RGB DN Image (Left) and Spectral Radiance image (Right) in May 14 th , 2013. Co Internship Report - PHAM Thi Thanh Hoa
1.2. Correction of Spectral Radiance to the 8 Reflectance at the Top of the atmosphere and to the Surface Reflectance We consider ground as a Lambertian surface, then: we obtain the reflectance at the TOA: (3) 2 L . d . S ES TOA E . Cos ( ) S s (4) Where: - Diffuse spectral reflectance; From formula (4), we acknowledge that this obtained v - View path transmittance from the Earth to the receiver; reflectance haven’t calibrated: S - View path transmittance from the Sun to the Earth; - The effect of atmosphere. E S - Solar spectral radiation; - The effect of topography d ES – Astronomical distance between the Sun and the Earth; - The effect of azimuth of the receiver on the satellite. S - Solar azimuth angle. Internship Report - PHAM Thi Thanh Hoa
1.2. Correction of Spectral Radiance to the 9 Reflectance at the Top of the atmosphere and to the Surface Reflectance Processing Steps: Internship Report - PHAM Thi Thanh Hoa
1.2. Correction of Spectral Radiance to the 10 Reflectance at the Top of the atmosphere and to the Surface Reflectance Practical Case for Hue: Raw Image (Left), Reflectance at TOA Image (Middle) and Reflectance at the Surface (Right). Internship Report - PHAM Thi Thanh Hoa
1.2. Correction of Spectral Radiance to the 11 Reflectance at the Top of the atmosphere and to the Surface Reflectance Statistical Assessment: Vegetation Spectral Profile at surface (left) and at TOA (right): VNREDSat-1 Image in May 14 th , 2013 Statistical Result DN 𝝇 𝑼𝑷𝑩 𝝇 𝑻𝑮 Mean 129.2872 0.148704 0.087790 Variance 1137.603 0.001546 0.001546 CV 0.260879 0.256666 0.444793 Internship Report - PHAM Thi Thanh Hoa
2. Calculation of some Physical Indices 12 of VNREDSat – 1A Images. Vegetation indices can be calculated directly from remote sensing images, and then are used for various purposes like vegetation-covering assessment, biomass assessment, crop monitoring, etc. Some Vegetation Indices: 𝑂𝐸𝑊𝐽 = 𝑂𝐽𝑆−𝑆 𝑂𝐽𝑆+𝑆 𝑂𝐽𝑆−𝑆 𝑇𝐵𝑊𝐽 = 𝑂𝐽𝑆+𝑆+𝑀 (1 + 𝑀) 𝑄𝑊𝐽 = 𝑂𝐽𝑆−𝑏𝑆−𝑐 𝑏 2 +1 Where: NIR: Near infrared spectral bands Red: Red spectral bands. a, b, L: parameters Internship Report - PHAM Thi Thanh Hoa
2. Calculation of some Physical Indices 13 of VNREDSat – 1A Images. NDVI: SAVI: SAVI NDVI Minimum: -0.2339 Minimum: -0.8127 Maximum: 0.7022 Maximum: 0.9145 Mean: 0.2582 Mean: 0.4598 Std Dev: 0.1327 Std Dev: 0.2661 Internship Report - PHAM Thi Thanh Hoa
2. Calculation of some Physical Indices 14 of VNREDSat – 1A Images. PVI: The values of parameters a and b can be deduced from the linearity of brightness of soil in PVI band 3 (red) and band 4 (nir) Minimum: -0.0423 Maximum: 0.4167 Mean: 0.1347 Std Dev: 0.0601 Internship Report - PHAM Thi Thanh Hoa
3. Preprocessing Methodology 15 ENVI tool named “ VNREDSat Calibration” under the function “Calibration Utilities” of Basic Tools. Internship Report - PHAM Thi Thanh Hoa
Conclusion 16 During this internship, there are two main matters: - Calibrating DN images due to the effect of receiver of the satellite and the atmosphere. - Calculating some vegetation indices: NDVI, SAVI, and PVI. The images which are corrected and treated by DOS 4 obtain higher quality since their variant indices are close to zero. Hence, the final image is more reliable when we need to use it for identifying threshold of objects on the surface, and managing volatility. IDL and ENVI are highly potential to dig deeper and develop more in the future. Internship Report - PHAM Thi Thanh Hoa
17 THANK YOU FOR YOUR ATTENTION! Internship Report - PHAM Thi Thanh Hoa
18 THANK YOU FOR YOUR ATTENTION! Internship Report - PHAM Thi Thanh Hoa
Recommend
More recommend
