Profile of dielectric constant of a substance or a surface indicates its electromagnetic parameters. The profile is associated with electric polarization, permeability with magnetic polarization, and conductivity with an electric current field. In the practice, the Synthetic Aperture Radar (SAR) and the Ground Penetrating Radar (GPR) are commonly utilized to determine how much velocity of a substance and its scattering profiles. However, information about the profile radar scattering mechanisms in tropical peatland is still limited. Therefore, we evaluated dielectric constant from the field using GPR and estimated its spatial variation from a dual-polarization Sentinel-1A type C-band SAR in Ogan Komering Ilir, South Sumatera Province, Indonesia. We measured dielectric constant at the two major types of land use, namely oil palm and acacia. Results indicated that the dielectric constant derived from SAR Sentinel-1A and GPR are affected by peat moisture. It increases as the peat moisture increases. Results show that during peat dry conditions, the profiles of dielectric constant derived from dual-pol Sentinel-1A images are relatively similar to the dielectric constant of peat in Siak Regency. It ranges between 31.78 and 59.3. The dielectric constant derived from GPR ranges between 69 and 70.
Synthetic Aperture Radar (SAR) is newest remote sensing technology that is not affected by meteorological conditions. This technology is particularly suitable for use in tropical regions such as Indonesia. In tropical peatland, Indonesia becomes the most important countries for peat areas and carbon stocks. However, this tropical peatland forest had been disturbed by fires, and become a national issue and an international issue. In disaster mitigation, identifying the existence of tropical peatland are needed. But this information is very limited. Therefore, we analysed backscattering value of VV and VH polarisation, and estimated dielectric constant from a dual-polarisation Sentinel-1A in Siak Regency, Riau Province, Indonesia. We also measured dielectric constant at four several types of land use (namely, forest, oil palm, shrubs, and agriculture) along with two types of peat conditions. Results indicated that the dielectric constant decreases as the land use become dry. Results show that the profiles of dielectric constant derived from dual-pol Sentinel-1A images have a high similarity to the direct approach using GPR, with a degree of similarity of 87.24%. The averaged dielectric constants of peat are lower than the peat in subtropics area and ranges between 41 and 68.
Changes in cloud cover and atmospheric aerosol loading strongly affect the diffuse proportion of solar radiation (R d /R g ). It has been reported that plant photosynthesis is more efficient under diffuse light conditions, but diffuse radiation (R d ) regimes in tropical peatland frequently subjected to largescale fires are poorly described, and there are few or no site-based datasets to date. Therefore, we continuously measured R d for more than three years at a burnt ex-forest on tropical peatland in Central Kalimantan, Indonesia. Daily R d /R g was significantly related to the clearness index (R g /R o ) with a linear threshold model. The model parameters showed that R d /R g under a clear sky is larger in tropical peatland with a humid climate than in Australia. Using the model, long-term variation in R d /R g for more than 12 years was estimated from R g measured above a nearby forest. As a result, R d /R g showed a seasonal variation with its minimum of 0.51 in June (the transition between the wet and dry seasons) and its maximum of 0.68 in October (the late dry season) on a monthly basis. The decreasing pattern from the late wet season to the early dry season corresponded to decreasing precipitation due to fewer clouds. In contrast, the increasing pattern through the latter half of the dry season was due to shading by smoke emitted through burning biomass and peat fires. In particular, during the El Niño droughts in 2002, 2006 and 2009, the monthly mean R d /R g rose above 0.72, because the ground was densely covered with smoke from large-scale fires.
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