Membuat Komposit Citra Landsat 8 dalam Earth Engine (GEE-8)

GEE Bagian 8 ini adalah kelanjutan dari GEE-7 yang sebelumnya dibahas dalam artikel Mencari Image Collections dalam Earth Engine (GEE-007). Jika Anda belum membacanya, baca dulu, 5 menit kok.

Ketika Anda menambahkan citra multi band dalam peta yang Anda buat, Earth Engine secara otomatis akan memilih tiga band pertama dalam citra tersebut dan menampilkannya sebagai merah, hijau, dan biru secara default (RGB). Contohnya adalah jika Anda menggunakan Landsat 8 yang kita cari sebelumnya di Image Collections.

Map.centerObject(citral8, 11);
Map.addLayer(citral8, {}, 'RGB');

Hasilnya buruk, kan? Perhatikan bahwa citra ini dipusatkan dengan zoom sebesar 11. Perhatikan juga bahwa citra ini divisualisasikan dengan menggunakan objek kosong ( {} ) untuk visualisasi-nya sehingga citranya divisualisasikan dengan tiga band pertama sebagai R G B. Setiap dari band ini pun direntangkan menjadi [0, 1] karena band-band ini memiliki format float. Berarti, band yang digunakan untuk R (merah) adalah band coastal aerosol, G (hijau) adalah band biru, dan B (biru) adalah band hijau. Untuk membuat komposit citra warna nyata (true color) Anda perlu menyatakan penggunaan band ini dalam line javascript Anda. Gunakan B4 untuk R, B3 untuk G, dan B2 untuk B. Untuk menggunakan sebuah band gunakan properti dari perintah band dari objek visualisasi. Untuk band apa saja yang ada dalam Landsat 8 Anda dapat melihar referensi berikut.

Anda juga perlu untuk memberikan nilai min dan max yang sesuai untuk memvisualisasikan nilai pantulan dari permukaan Bumi yang Anda targetkan. Biasanya kita menggunakan 0.3 sebagai max serta 0 sebagai min untuk digunakan sebagai nilai default. Kombinasi dari parameter ini dapat dinyatakan dalam perintah berikut :

var visualisasi = {bands: ['B4', 'B3', 'B2'], max: 0.3};
Map.addLayer(citral8, visualisasi, 'komposit warna nyata');

Hasilnya akan terlihat seperti gambar di bawah ini. Perhatikan bahwa kode ini ditujukan pada objek visualisasi. Objek ini akan sangat bermanfaat ketika anda membuat visualisasi apapun dalam Earth Engine.

Landsat 8 TOA reflectance yang ditampilkan dalam komposit warna nyata

Cobalah bermain menggunakan band lain dalam membuat komposit. Cobalah dengan menggunakan kombinasi B5, B4, dan B3 untuk citra komposit false color.

// false color
var visualisasi = {bands: ['B5', 'B4', 'B3'], max: 0.3};
Map.addLayer(citral8, visualisasi, 'komposit false color');
Tampilan citra Landsat 8 false color

Updated:

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