Surface Reflectance and Spectral Index Lalu Muhamad Jaelani, PhD

Radiometric Correction Digital Number -> Top of Atmosphere Radiance (Ltoa) or Reflectance (ρtoa) Formula: Gain-offset Lmax-Lmin or ρmax-ρmin Radiometric Calibration Removing atmospheric effect from total signal received by sensor Ltoa or ρtoa ->Lboa or ρboa (SR, surface reflectance) Atmospheric Correction

Pada tanggal 23 Desember 2014, USGS mengeluarkan produk level tinggi untuk surface reflectance (Reflectance-BOA). Dengan keluarnya produk ini, maka kendala koreksi atmosfer yang harus dilakukan untuk mengubah reflectance at satellite (reflectance-TOA) menjadi surface reflectance, menjadi berkurang Radiative transfer model yang digunakan oleh USGS untuk melakukan  koreksi atmosferik (atmospheric correction) adalah: – 6S simulation model untuk Landsat 4-7 , dan – Internal algorithm untuk Landsat 8.

L8-L1T Format: Digital Number Automatically converted to radiance if opened from MTL file (in BEAM VISAT)

L8-ρtoa Format: Digital Number Reflectance (band 1-9)= DN/10000

L8-SR Format: Digital Number Reflectance= DN/10000

Atmospheric Correction Before After

spectral indices Vegetation Indices (VI) Normalized Difference Vegetation Index (NDVI) Enhanced Vegetation Index (EVI) Soil Adjusted Vegetation Index (SAVI) Modified Soil Adjusted Vegetation Index (MSAVI) Normalized Difference Moisture Index (NDMI) Normalized Burn Ratio (NBR) Normalized Burn Ratio 2 (NBR2) Selain itu, akan diluncurkan produk berikut: Land Surface Temperature CDR Burned Area Extent ECV Surface Water Extent ECV Snow Covered Area ECV

L8-Spectral Index Format: Digital Number SI= DN/10000

Vegetation Index Normalized Difference Vegetation Index (NDVI) Landsat 4-7: NDVI = (Band 4 – Band 3) / (Band 4 + Band 3). Landsat 8: NDVI = (Band 5 – Band 4) / (Band 5 + Band 4).

Enhanced Vegetation Index (EVI) Landsat 4-7: EVI = (Band 4 – Band 3) / (Band 4 + 6 * Band 3 – 7.5 * Band 1 + 1). Landsat 8: EVI = (Band 5 – Band 4) / (Band 5 + 6 * Band 4 – 7.5 * Band 2 + 1).

Soil Adjusted Vegetation Index (SAVI) Landsat 4-7: SAVI = ((Band 4 – Band 3) / (Band 4 + Band 3 + 0.5)) * (1.5). Landsat 8: SAVI = ((Band 5 – Band 4) / (Band 5 + Band 4 + 0.5)) * (1.5).

Modified Soil Adjusted Vegetation Index (MSAVI) Landsat 4-7: MSAVI = (2 * Band 4 + 1 – sqrt ((2 * Band 4 + 1)2 – 8 * (Band 4 – Band 3))) / 2. Landsat 8: MSAVI = (2 * Band 5 + 1 – sqrt ((2 * Band 5 + 1)2 – 8 * (Band 5 – Band 4))) / 2.

Normalized Difference Moisture Index (NDMI) Landsat 4-7: NDMI = (Band 4 – Band 5) / (Band 4 + Band 5). Landsat 8: NDMI = (Band 5 – Band 6) / (Band 5 + Band 6).

Normalized Burn Ratio (NBR) Landsat 4-7: NBR = (Band 4 – Band 7) / (Band 4 + Band 7). Landsat 8: NBR = (Band 5 – Band 7) / (Band 5 + Band 7).

Normalized Burn Ratio 2 (NBR2) Landsat 4-7: NBR2 = (Band 5 – Band 7) / (Band 5 + Band 7). Landsat 8: NBR2 = (Band 6 – Band 7) / (Band 6 + Band 7).

http://lmjaelani.com/2015/01/landsat-terkoreksi-efek-atmosfer/ http://lmjaelani.com/2015/05/produk-indeks-vegetasi-landsat/

Background Algorithm ρ = reflectance value For Landsat and others satelite images, need to convert DN to ρ, first

MODIS and LANDSAT L (canopy background)=1, C1 = 6, C2 = 7.5, and G (gain factor) = 2.5.

NDVI EVI correct aerosol influence in NDVI

NDVI_SWIR and EVI_SWIR SWIR = Shortwave Infra Red =1,5-q,7 micro m