The visual identification of mangrove forests is greatly constrained by combinations of RGB composite. This research aims to determine the best combination of RGB composite for identifying mangrove forest in Segara Anakan, Cilacap using the Optimum Index Factor (OIF) method. The OIF method uses the standard deviation value and correlation coefficient from a combination of three image bands. The image data comprise Landsat 8 imagery acquired on 30 May 2013, Sentinel 2A imagery acquired on 18 March 2018 and images from SPOT 6 acquired on 10 January 2015. The results show that the band composites of 564 (NIR+SWIR+Red) from Landsat 8 and 8a114 (Vegetation Red Edge+SWIR+Red) from Sentinel 2A are the best RGB composites for identifying mangrove forest, in addition to those of 341 (Red+NIR+Blue) from SPOT 6. The near-infrared (NIR) and short-wave infrared (SWIR) bands play an important role in determining mangrove forests. The properties of vegetation are reflected strongly at the NIR wavelength and the SWIR band is very sensitive to evaporation and the identification of wetlands.

Abstract. Diffuse attenuation coefficient, Kd(λ), has an empirical relationship with water depth, thus potentially to be used to estimate the depth of the water based on the light penetration in the water column. The aim of this research is to assess the relationship of diffuse attenuation coefficient with the water constituent and its relationship to estimate the depth of shallow waters of Air Island, Panggang Island and Karang Lebar lagoons and to compare the result of depth estimation from Kd model and derived from Landsat 8 imagery. The measurement of Kd(λ) was carried out using hyperspectral spectroradiometer TriOS-RAMSES with range 320 -950 nm. The relationship between measurement Kd(λ) on study site with the water constituent was the occurrence of absorption by chlorophyll-a concentration at the blue and green spectral wavelength. Depth estimation using band ratio from Kd(λ) occurred at 442,96 nm and 654,59 nm, which had better relationship with the depth from in-situ measurement compared to the estimation based on Landsat 8 band ratio. Depth estimated based on Kd(λ) ratio and in-situ measurement are not significantly different statistically.Depth estimated based on Kd(λ) ratio and in-situ measurement are not significantly different statistically. However, depth estimation based on Kd(λ) ratio was inconsistent due to the bottom albedo reflection because the Kd(λ) measurement was carried out in shallow waters. Estimation of water depth based on Kd(λ) ratio had better results compared to the Landsat 8 band ratio.

The flank collapse of Anak Krakatau on 22 December 2018 caused massive topography losses that generated a devastating tsunami in Sunda Strait, which then followed by eruptions that progressively changed the topography and structure of Anak Krakatau. Here, we investigated topography and structural changes due to the December 2018 flank collapse and the following eruptions by using high resolution Digital Elevation Model (DEM) before and after the events and sentinel 1A satellite image post-flank collapsed. Results show that the volumetric losses due to the 22 December 2018 flank collapsed is ~127 x 106 m3, while the following eruptions caused ~0,8 x 106 m3 losses. Structural investigation suggests two structures that may act as failure planes. The first structure is located at the western part of volcanic edifice that associated with hydrothermal alteration and the second failure is an old crater rim which delineated an actively deform volcanic cone.

Nilai koefisien diffuse atenuasi Kd(λ) yang berasal dari pengukuran downwelling irradiance Ed(λ) merupakan salah satu parameter penting dalam oceanografi yang memberikan informasi mengenai ketersediaan cahaya dan tingkat penetrasi cahaya di dalam kolom air yang memberikan gambaran mengenai tingkat kecerahan, fotosintesis dan proses biologi lainnya. Informasi mengenai koefisien diffuse atenuasi memegang peranan penting dalam pengembangan algoritma Bio-Optik pada data satelit Ocean Color. Tujuan dari penelitian ini adalah untuk menjelaskan variabilitas dari koefisien diffuse atenuasi di perairan dangkal Karang Lebar, pulau Air dan Panggang dengan menggunakan sensor irradiace hyperspectral radiometer TriOS-RAMSES dengan cakupan rentang panjang gelombang 320 hingga 950 nm dengan resolusi spektral 3.3 nm. Pengukuran in situ dilakukan dengan menurunkan sensor irradiance di setiap kedalaman secara vertikal pada kolom air. Secara keseluruhan hasil pengukuran menunjukkan bahwa nilai Kd(λ) memiliki pola dimana pada region panjang gelombang 380-480 nm akan menurun dan akan meningkat kembali hingga pada region panjang gelombang merah 560-760 nm. Nilai Kd(λ) di bagian dalam gobah ditemukan lebih tinggi dibandingkan di bagian luar gobah dengan perbedaan yang signifikan terjadi di region panjang gelombang merah, perbedaan signifikan nilai Kd(λ) juga terjadi di ketiga wilayah (F = 5.581 > F critical = 5.554) dimana masing-masing area memiliki karakteristik yang berbeda-beda. Secara dominan, nilai Kd(λ) dipengaruhi oleh serapan klorofil-a dengan R2 = 0.808 dibandingkan dengan hamburan dari muatan padatan terlarut dibuktikan dengan R2 = 0.043. Nilai Kd(λ) pada rentang panjang gelombang sinar tampak (400-700 nm) dapat memberikan gambaran mengenai jangkauan penetrasi cahaya sinar tampak yang bisa dideteksi oleh satelit dengan satuan satu kedalaman optik. Hubungan nilai Kd(λ) dengan satu kedalaman optik dijelaskan secara eksponensial dengan persamaan Kd(400-700nm) = 0.375*exp(-0.095*1ζ) dengan koefisien determinasi R2 = 0.97.