GaoFen-3 (GF-3) is the first fully polarimetric C-band synthetic aperture radar (SAR) satellite in China. Interferometric observation is an important capability of GF-3. However, the long temporal baseline is a great challenge for repeat-pass interferometric synthetic aperture radar (InSAR) processing, especially over mountainous areas. Phase noise and complex topography make phase unwrapping difficult. This paper proposes a step-wise approach for high-resolution InSAR data processing focusing on facilitating phase unwrapping. First, the coarse GF-3 digital elevation model (DEM) is reconstructed by InSAR processing with multilooking of large looks, which is used to suppress phase noise. Second, the coarse GF-3 DEM is used to remove the terrain phase from the InSAR phase with multilooking of small looks, which can reduce phase gradient and improve the accuracy of phase unwrapping. After several iterations, the GF-3 DEM is finally inversed with multilooking of 2 looks, which is of high resolution and high accuracy. The performance of GF-3 C-band InSAR data on the extraction of DEM is examined over a deciduous forested area with the proposed method. The root-mean-square error of the extracted GF-3 DEM is 3.78 m in comparison with the LiDAR DEM.
Forest covers about 30% of earth surface, which plays an important role in global forecast and carbon cycle.
Monitoring forest biomass, and retrieving soil moisture at forest area, are the main goals of most passive microwave
sensors on satellite missions. L-band is the most sensitive frequency among all the frequencies due to its good penetration
ability. Because of its variety of the size of scattering components, the complicated structures and species of forest, it is
difficult to describe the scattering and attenuation characters of forest in modeling microwave emission at forest area.
In this paper, we studied the emissivity and transmissivity of deciduous forest at L(1.4GHz) by model simulation and
field experiment. The microwave emission model was based on Matrix-Doubling algorithm. The comparison between
simulated emissivity and measured data collected during an experiment at Maryland, USA in 2007 was good.
Since theoretical model like Matrix-Doubling is too complicated to be used in retrial application, we mapped the
results of Matrix-Doubling to a simple 0th-order model, also called ω-τ model, by setting the simulated emissivity to be the
emissivity of 0th-order model at the same environment, which 2 unknown variables---opacity τ and effective single
scattering albedo ω need to be determined.
To valited τ (transmissivity of forest) simulated by Matrix-Doubling, we took an deciduous forest experiment by an L
band microwave radiometer under trees at JingYueTan area, Changchun, Jilin Province in April to June in 2014. Thus the ω
of forest can be determined.
The matching results are presented in this paper. The relationship between LAI and forest microwave characters are
In this study, a bare surface soil moisture retrieval algorithm independent of the soil temperature is developed for use with advanced microwave scanning radiometer-Earth observing system measurements. The quasiemissivity is parameterized as the ratio of the brightness temperature in the other channels to that in the 36.5 GHz vertical (V-) polarization in order to correct the soil temperature effects in the estimation of soil moisture. To analyze the surface roughness effect on quasiemissivity, a simulation database covering a large range of soil properties is generated. The advanced integral equation model (AIEM) is used to simulate the soil emissivities at different frequencies. The parameters describing the soil roughness effect on quasiemissivity at two polarizations are found to be expressed by a linear function. Using this relationship and the quasiemissivity at two polarizations, the surface roughness effect is minimized in the estimation of the soil moisture. Thus, soil moisture can be estimated using the brightness temperatures at a given frequency in the V- and horizontal (H-) polarizations and at 36.5 GHz of V-polarization. Compared with the data simulated using AIEM, the algorithm has a root-mean-square error (RMSE) of approximately 0.009 cm3/cm3 for the volumetric soil moisture. For validation, a controlled field experiment is conducted using a truck-mounted multifrequency microwave radiometer. Moreover, the experimental data acquired from the Institute National de Recherches Agronomiques (INRA) field experiment are also used to evaluate the accuracy of the algorithm. The RMSE is approximately 0.04 cm3/cm3 for these two experimental data. In order to analyze the performance or capability of this algorithm using satellite data, the soil moisture derived from WindSat data using this algorithm is compared to the Murrumbidgee soil moisture monitoring network dataset. These results indicate that the newly developed inversion technique has an acceptable accuracy and is expected to be useful for application for bare surface soil moisture estimation.
Forest is important in global carbon cycle and has potential impact on global climatic change.
Whether the soil moisture under forest area can be detected by microwave emission signature is
unknown due to the dense forest cover. Also, the relationship between forest biomass and its
microwave emissivity and transmissivity is of interest to be studied.
The microwave emission contribution received by the radiometer above the forest canopy
comes from both the soil surface and vegetation layer. In this study, a high-order emission model,
Matrix-Doubling, was employed to simulate the emissivity of a young deciduous forest. A field
experiment before and after watering the deciduous tree stand was carried in June 5, 2011 in
Baoding, China to verify the model, and to measure the tree transmissivity. A tree was selected to
be cut to measure the tree parameters and weighed its biomass. Assuming the forest as a
non-scattering medium, the effective single-scattering albedo is obtained for 0th-order model by
fitting the same emissivity from Matrix-Doubling model. For lower albedo which could be
ignored, transmissivity of trees can be deduced by measured Brightness Temperatures before and
after watering the underlying soil. The relationship between forest biomass and its transmissivity
is presented in this paper.
In soil moisture retrieval by microwave remote sensing technology, vegetation effect is important, due to its emission upward as well as masking the soil surface contribution. Because of good penetration characteristics through crop at low frequencies, L-band is often used, where crop is treated as a uniform layer, and 0th-order Brightness Temperature model is used. Higher frequencies upper than L-band, the frequencies both on NASA AQUA AMSR-E and FY-3 to be launched next year in CHINA, may be more informative in SM retrieval. The multiple-scattering effects inside crop and that between crop layer and soil surface will be increasing when frequencies go higher from L-band. In this paper, a Matrix-Doubling model that account for multiple-scattering based on ray tracing technique is used to simulate the microwave emission of vegetated-surface at C- and X-band. The orientation and size of crop element such as leaves and cylinders are accounted for in crop layer, and AIEM is used for calculation of ground surface scattering. Simulation results from this model for corn and SGP99 experiment data are in good agreement. Since complicated theoretical model as used in this paper involves too many parameters, to make SM retrieval more directly, corresponding terms from the developed model are matched with 0th-order,so as to derive effective single scattering albedo and vegetation opacity at C- and X-band.
Many studies on soil moisture retrieval at vegetated area from microwave radiometry data assume a simple model of vegetation, which is characterized by vegetation volume fraction, effective dielectric constant, plant moisture content, etc. In this study, a radiative transfer model is used to model the emissivity and transmissivity of forest canopy, which is more realistically characterized as a volumetric medium consisting of discrete scatters (leaves, stems, tree branches, and trunks). To facilitate the soil moisture inversion from radiometry data, the unknown variables need to be reduced. The possibility of fitting the modeled emissivity and transmissivity of vegetation canopy into simple equations, and the relationships of these parameters between different microwave radiometry frequencies were studied and the results are presented in this paper.