Spektrum Gelombang
Pengantar Synthetic Aperture Radar
Bambang H. Trisasongko Department of Soil Science and Land Resources, Bogor Agricultural University. Bogor 16680. Indonesia. Email:
[email protected]
Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
Courtesy: Geography, Utah
Penginderaan Elektromagnetik • Pasif: – Gelombang Tampak dan Inframerah: Landsat, SPOT XS
Gelombang Mikro - Pasif • TRMM, ESMR, dll: analisis meteorologi/iklim
– Gelombang Mikro: TRMM (Tropical Rainfall Measuring Mission) • Aktif: – Gelombang Tampak dan Inframerah: LIDAR (Light Detection and Ranging) – Gelombang Mikro: Radar (RAR: Real Aperture Radar, SAR: Synthetic Aperture Radar)
http://trmm.gsfc.nasa.gov Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
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Gelombang Mikro - Aktif
Gelombang Mikro - Aktif
• Bukan Pencitra: Plan Position Indicator (PPI), Altimeter, Scatterometer
• RADAR (Radio Detection and Ranging) merupakan sensor penginderaan jauh aktif yang beroperasi pada spektrum gelombang mikro
• Tiga mekanisme penting: – Pengiriman Sinyal (Tx) – Penerimaan Sinyal (Rx) – Pengukuran kekuatan sinyal balik; jeda waktu antara pengiriman dan penerimaan sinyal; perilaku temporal • Pencitra (Imaging Radar): Side-Looking Radar
Soil Science and Land Resources, Bogor Agricultural University ~~~
Gelombang Mikro – Aktif: Radar c f0 dimana panjang gelombang (m) c kecepatan cahaya (m/sec) f 0 frekuensi transmisi radar (Hz)
Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
Keuntungan • Pengaruh atmosfer minimum, cocok untuk daerah tropis • Dapat beroperasi siang dan malam • Cocok untuk misi kritikal waktu: militer, bencana alam dan estimasi ketersediaan pangan • Sensitif pada sifat dielektrik (estimasi kelembaban) • Sensitif pada kekasaran permukaan (kecepatan angin) • Sensitif pada bahan buatan manusia • Penetrasi permukaan (panjang gelombang tertentu)
Soil Science and Land Resources, Bogor Agricultural University ~~~
Courtesy: NM. Short, Sr
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Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
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Kerugian
Efek Speckle
• Interpretasi yang berbeda dengan optik; membutuhkan SDM yang spesifik • Efek spekel (noise) • Efek Atmosfer pada frekuensi tertentu • Data lebih terbatas dari optik; kajian menjadi sangat minim • Distorsi; membutuhkan ketrampilan geocoding yang tinggi
Soil Science and Land Resources, Bogor Agricultural University ~~~
Efek Atmosfer
L-band
Soil Science and Land Resources, Bogor Agricultural University ~~~
Sistem SAR Spaceborne
X-band
Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
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Sistem Pencitraan
Mekanisme Perolehan Data
• Miring, bukan Nadir (atau off-Nadir) • Arah pencitraan: – Slant: tegak lurus arah wahana – Azimuth: sejajar arah wahana • • • • •
A= arah terbang B= nadir C= lebar sapuan (swath) D= arah slant E= arah azimuth
RADIO DETECTION AND RANGING
Jarak Miring (Slant Range)
SR Soil Science and Land Resources, Bogor Agricultural University ~~~
Geometri Pencitraan • Slant Range vs Ground Range • Pada sensor: Look angle + Depression angle = 90 derajat • Pada Bumi: – Incidence Angle
ct 2
Soil Science and Land Resources, Bogor Agricultural University ~~~
Slant vs Ground Range Arah Range
Arah Azimuth
Jenis Data yang Tersedia Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
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Look Angle
Incidence Angle
• Dapat dimanfaatkan untuk studi kekasaran permukaan (morfometri) • Dikatakan “halus” bila
h rms
25 cos Look angle
• Dikatakan “kasar” bila
h rms
4 cos
Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
Resolusi Spasial: Arah Range Rr
Θd = depression angle
c.t 2 cos
t = pulse duration
Resolusi Range dan Azimuth
Dikenal dengan istilah pulse length (PL) PL kecil >> resolusi tinggi, tapi energi iluminasi rendah
GR θd SR
Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
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Resolusi Spasial: Arah Azimuth •
•
Resolusi arah azimuth ditentukan oleh: – Ground range – Lebar sinar (beamwidth)
• •
• SAR mensintesis resolusi dengan: – Antena yang pendek – Akuisisi simultan dan kontinyu
Raz = GR . BW
Bw
Real Aperture Radar vs. Synthetic Aperture Radar
– Simulasi antena panjang melalui Digital Signal Processing yang kompleks
PanjangAnt ena
Real Aperture Radar Synthetic Aperture Radar
Soil Science and Land Resources, Bogor Agricultural University ~~~
Synthetic Aperture Radar
Soil Science and Land Resources, Bogor Agricultural University ~~~
© CCRS
Radar Equation
Tiga komponen utama yang menentukan kekuatan sinyal balik yang direkam: • Sistem SAR • Geometri pencitraan • Interaksi gelombang dengan objek Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
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Sifat Hamburan Balik • A= Spekular (specular, odd-bounce) • B= baur (diffuse) • C= Corner reflection (even-bounce)
Distorsi • Distorsi Skala akibat posisi pencitraan yang miring
Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
Distorsi
• Distorsi Relief: – Foreshortening
– Layover Look angle 23 degrees
– Shadowing Look angle 36 degrees
Look angle 47 degrees Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
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Jenis Data dan Pendekatan Analisis SAR
Soil Science and Land Resources, Bogor Agricultural University ~~~
Jenis Data •
•
• •
Soil Science and Land Resources, Bogor Agricultural University ~~~
Range-Doppler processing
Raw Data – Slant range; Data dalam bilangan kompleks: Amplitude dan Phase – Setiap baris terdiri dari sinyal balik dari satu pulse > satu obyek yang sama akan terlihat pada berbagai baris citra – Level 0 – Tidak diperuntukkan bagi pengguna umum (end user) – Membutuhkan perangkat khusus SAR Processor Single Look Complex (SLC) – Slant Range; Masih dalam bilangan kompleks – Mengkombinasikan obyek yang terpisah dalam beberapa baris menjadi satu tampilan; Tampilan dalam arah Range masih terkompresi – Level 1 (L 1.0 atau L 1.1) Multi-Look – Ground Range; Masih dalam Bilangan Kompleks Intensity Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
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Pendekatan Analisis • • • • • • •
Hamburan Balik
Hamburan Balik (backscatter) Komposit Multitemporal Interferometri (InSAR, D-InSAR, PS-InSAR) Polarisasi (PolSAR): Dual Polarimetric; Fully Polarimetric Compact Polarimetry (CP) Polarimetric SAR Interferometry (PolInSAR) Polarimetric Tomography (PolTomSAR)
Trisasongko et al. 2007. Sensing and Imaging vol. 8. © Springer-verlag, USA Soil Science and Land Resources, Bogor Agricultural University ~~~
Komposit Multitemporal
Soil Science and Land Resources, Bogor Agricultural University ~~~
Interferometri (InSAR)
Raimadoya et al. Jurnal Ilmu Tanah dan Lingkungan 2005
Raimadoya et al. IGTE-2, 2008 Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
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Polarisasi Ganda
Raimadoya and Trisasongko. 2007. POLINSAR. ISBN No. 92-9291-208-7 Soil Science and Land Resources, Bogor Agricultural University ~~~
Compact Polarimetry
Polarisasi Penuh
Trisasongko et al. 2006. Mine Water and The Environment. © Springer-verlag. USA Soil Science and Land Resources, Bogor Agricultural University ~~~
Polarimetric SAR Interferometry • Aplikasi estimasi tinggi pohon
Fully polarimetric (2 mode Tx, Rx)
Compact polarimetric (1 mode Tx, 2 mode Rx)
Soil Science and Land Resources, Bogor Agricultural University ~~~
Soil Science and Land Resources, Bogor Agricultural University ~~~
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Berpikir adalah Setengah Ibadah
Soil Science and Land Resources, Bogor Agricultural University ~~~
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