Post on 07-Dec-2015
description
Koreksi Atmosfer
Lalu Muhamad Jaelani, Ph.DLMJaelani.com
2
No atmosphere ρtoa
ρ w
Data yg diperoleh
Mengapa Koreksi Atmosfer diperlukan?
≠
0
102030405060708090
100
Troposphere
Stratosphere
Mesosphere
Thermosphere
Altit
ude
(km
)
O3, N2, (NH4)2SO4
O2, H2O
ρ r
ρ a
++
≈
Data yg diinginkan Water
Sun sensor
3
413 443 490 510 560 620 665 681 709 7540
0.0100000000000001
0.0200000000000002
0.0300000000000003
0.0400000000000003
Lake Kasumigaura
Wavelength (nm)
Rem
ote
Sens
ing
Ref
lect
ance
(sr-
1)
Data yang diperoleh (direkam oleh sensor)
Data yang diinginkan
Apa yang dimaksud dengan Koreksi Atmosfer?
Efek
Atm
osfe
r
= menghilangkan efek atmosfer dari data yang direkam oleh sensor
4
Teori Dasar
)()()()()( wArtoa t
Dari data satellite Dapat dihitung dari model
2 unknowns
TOA reflectance Aerosol scattering Water leaving reflectance
Rayleigh scattering transmittance
Koreksi Atmosfer di Air Jernih
NASA Ocean Biology Processing Group
5
Air Jernih ρw(NIR) ≈ 0.0
Dapat diasumsikan bahwa ρw pada kanal NIR (779 nm and 865 nm) = 0.0
Near Infra Red (NIR)
6
Mendapatkan Aerosol Scattering untuk kanal NIR di air jernih
)()()()()( NIRNIRtNIRNIRNIR wArtoa
)()()( NIRNIRNIR Artoa
One unknown
NIR bands = 779 and 865 nm
zero
at other wavelengths
at other wavelengths
Proses Koreksi Atmosfer di Air Jernih
ρA(779)ρA(865)
ρa(779)ρa(865)
)(
)()()()(
tArtoa
w
LUT
LUT )865,(
)865,779()865(
)779(
a
a
Aerosol type/model
Atmospheric corrected reflectance
Multiple scattering
Single scattering
ρa(λ)ρA(λ)Extent epsilon to
other wavelengths
8
412 443 490 510 560 620 665 681 709 754 762 779 865 885 9000
0.00500000000000001
0.01
0.015
0.02 Lake Kasumigaura
Wavelength (nm)
Rem
ote
Sens
ing
Ref
lect
ance
(sr-
1)Koreksi Atmosfer di Air Keruh (Turbid Water)
The spectral value at near infrared wavelength≠ 0
two unknowns
)()()()()( wArtoa tNear Infra Red (NIR)
Masalah Koreksi Atmosfer di Air Keruh
)()()()()( wArtoa t
One equation has two unknowns.
How to solve this problem ?
10
Several approaches to solve the above problem
)()()()()( wArtoa t
Two unknowns1. Directly predict the aerosol reflectance using different assumption [Ruddick et. al. (2000); Hu et. al. (2000); Wang and Shi (2007); Guanter et. al. (2007, 2010)]
2. Estimate water leaving reflectance firstly, and then estimate aerosol reflectance [Stumpf et. al. (2003); Bailey et. al (2010); Wang et. al. (2012)]3. Estimate water leaving reflectance and aerosol reflectance simultaneously [Schroeder et. al. (2007); Doerffer & Schiller (2007,2008); Kuchinke et al. (2009a, 2009b)]
Koreksi Atmosfer Sederhana
• Metode DOS (Dark Object Substraction)• Metode Radiative Transfer 6SV (Second
Simulation of a Satellite Signal in the Solar Spectrum – Vector)
DOS
• Data dalam format Reflektan-Sensor (ρtoa)• Nilai Pixel Minimum (NPM) dari citra harusnya
adalah NOL• Cari NPM minimum (> nol)• Semua Pixel dikurangi NPM• Hasil akhir berupa reflektan-permukaan (ρboa)
6SV
• Data dalam format radian,• Citra dikoreksi dengan menggunakan rumus:
• acrλ=yλ/(1.+xcλ*yλ)
• yλ=xaλ*( Lλ)-xbλ; • acrλ adalah reflektan-permukaan, Lλ adalah radian.• Parameter koreksi diperoleh dengan menjalankan perangkat
lunak 6SV berbasis web yang ada di http://6s.ltdri.org/. • Untuk mendifinisikan konsentrasi dari aerosol, digunakan
parameter meteorologi berupa horizontal visibility yang dapat dimasukkan secara langsung dalam 6SV.
6S input for ALOS-VNIR2
• Geometrical conditions
6S input for ALOS-VNIR2
• Geometrical conditions– Month =9 (year=2010)– Day=1– Solar Zenith Angle =90-Solar Elevation Angle=90-
61.88=28.12 – Solar Azimuth Angle=57.37– Sensor Zenith Angle = 0 (Img_PointingAngle)– Sensor Azimuth Angle =12
(Img_SceneCenterOrientation)
Visibility
• http://www.wunderground.com/history/airport/WARR/2010/9/1/DailyHistory.html?req_city=Surabaya&req_state=&req_statename=Indonesia&reqdb.zip=00000&reqdb.magic=9&reqdb.wmo=96933
• Total second 9660 > jam 9.40• 5.0 km
Band 1• atmospheric correction result *• * ----------------------------- *• * input apparent reflectance : 0.100 *• * measured radiance [w/m2/sr/mic] : 52.386 *• * atmospherically corrected reflectance *• * Lambertian case : -0.00674 *• * BRDF case : -0.00674 *• * coefficients xa xb xc : 0.00603 0.32266 0.14326 *• * y=xa*(measured radiance)-xb; • acr=y/(1.+xc*y)
Band 1• atmospheric correction result *• * ----------------------------- *• * input apparent reflectance : 0.100 *• * measured radiance [w/m2/sr/mic] : 52.386 *• * atmospherically corrected reflectance *• * Lambertian case : -0.00674 *• * BRDF case : -0.00674 *• * coefficients xa xb xc : 0.00603 0.32266 0.14326 *• * y=xa*(measured radiance)-xb; • acr=y/(1.+xc*y)