Kari Heiska

Backscattering properties of boreal forests at the C- and X-bands

The backscattering properties of boreal forests are studied using empirical airborne and spaceborne radar data from Finland. Airborne measurements were carried out in the summer of 1992 by the HUTSCAT scatterometer at the Teijo test area in southern Finland. The HUTSCAT scatterometer is an eight-channel helicopter-borne profiling radar operating at the C- and X-bands. The ranging capability of the HUTSCAT scatterometer was employed in the semiempirical modeling of forest backscatter. The backscatter profile information was used in the analysis of the canopy transmissivity and the canopy backscattering coefficient by distinguishing backscattering contributions from the canopy and the ground. Additionally, ERS-1 C-band satellite SAR measurements were obtained for the Teijo test area and for the reference test area in Sodankyla in northern Finland. The radar results were compared with operational ground-based forest assessment data on forest compartments (stands) of the area. The key parameter investigated was the stem (bole) volume per hectare. The results obtained show the behavior of the canopy transmissivity and the canopy backscatter as a function of stem volume (directly related to the forest biomass). The influence of seasonal and diurnal changes on, and the effects of the changes in soil moisture to the backscattering coefficient were also investigated. >

Radar-based forest biomass estimation

Abstract The potential of radar-based tree biomass estimation has been studied using polarimetric SAR data from the Freiburg test site of the MAESTRO I Campaign and scatterometer data from a test site in Finland. Using the Freiburg SAR data and polarizaiton synthesis, the most suitable polarization combination was obtained. In P band, the maximum correIalions, which were found ncar the linear H V polarization, were up to 0·75. In the Finnish test site, a strong negative correlation “correlation coefficient -0·65” existed between the pine biomass and X-VV backscatter. When the combination of X and C bands “measured by the HUTSCAT seatterometer” was used, a correlation coefficient of 0·81 was obtained.

Mixing rules and percolation

Abstract The connection between percolation and dielectric mixing rules is the focus in this study. Percolation is identified as an abrupt change in permittivity or conductivity of a heterogeneous material as the volume fraction changes. It is shown that mixing rules, that can be presented in a compact form in a general mixing formula, are able to predict percolation. The connection between the mixing rule and its percolation threshold is found to be a simple law. The conductivity percolation obeys the same threshold. Numerical illustrations confirm the results. Also the effect of the spatial dimension of the mixture is analyzed.

Backscattering properties of boreal forests at C- and X-bands

The backscattering properties of boreal forests are studied using empirical airborne and spaceborne radar data from southern Finland. Airborne measurements were carried out in the summer 1992 by the HUTSCAT scatterometer. The HUTSCAT seatterometer is an 8-channel helicopter-borne profiling radar operating in Cand X-bands. Additionally, ERS-1 C-band satellite SAR measurements were obtained for the test area. The radar results were compared against operational ground-based forest assessment data on forest compartments (stands) of the area. The key parameter investigated was the stem (bole) volume per hectare, which is a parameter directly related to the biomass of the forest. The backscatter profile information was employed in the analysis of the canopy transmissivity and the canopy backscattering coefficient by separating backscattering contributions from the canopy and the ground.<<ETX>>

Application of ERS-1 SAR data in large area forest inventory

The National Forest Inventory of Finland (NFI) exploits satellite image data (Landsat TM) and digital elevation data in addition to ground measurements. The main purpose is to have estimates for essentially smaller areas (e.g. for some 1000 hectares) than what is possible with ground measurements only. The main objective of the study is to test the applicability of SAR images of ERS-1 together with other information sources, e.g. HUTSCAT, in estimating forest resources in large areas, and, if possible, to develop an operative forest inventory system which utilizes SAR-data.<<ETX>>

Statistics of backscattering source distribution of boreal coniferous forests at C- and X-band

The aim of this investigation is to describe the statistical backscattering properties of boreal coniferous forests at C- and X-band. The backscattering contribution of the crown, ground and several crown layers are dealt with separately. Preliminary results of the study are reported.<<ETX>>

Diurnal variation of backscattering properties of pine trees at C- and X-band

The behavior of the backscattering coefficient of a pine tree canopy was monitored at C- and X-band, VV, HH, VH and HV polarizations over a period of 24 hours in August 1993. By using their HUTSCAT ranging scatterometer, the authors could measure separately the total backscattering coefficient, the ground contribution and the canopy contribution. The incidence angle was 40/spl deg/ off nadir and the radar system was moved along a rail in order to obtain enough independent samples. The volumetric moisture of a tree trunk and ground surface (0 to 15 cm) along with the air temperature and total solar radiation was monitored as well. The backscattering coefficient for various frequency/polarization combination was compared with the ground truth. The results indicate that the diurnal behavior of the backscattering coefficient at C-band is different from that at X-band.<<ETX>>

Seasonal effects on C- and X-band backscattering properties of Finnish boreal forests

The seasonal changes of the backscattering properties of boreal forests are investigated by applying (1) a semi-empirical C- and X-band forest backscattering model and (2) multi-temporal ERS-1 SAR data from several test sites in Finland. The results are presented as a function of forest stem volume (which is closely related to forest biomass). The empirical modeling of forest canopy backscattering and extinction properties is based on the high-resolution ranging scatterometer (HUTSCAT) data. The response of ERS-1 SAR data to forest stem volume is investigated by employing the National Forest Inventory test sites that cover the ERS-1 test areas in a regular pattern. The model results and ERS-1 data show that the correlation of radar response to forest biomass may be positive, negative or about zero. This variation is primarily caused by the changes in soil and vegetation moisture, and by the seasonal snow-cover.<<ETX>>

Laboratory and Tower-Based Microwave Measurements of Spruce Defoliation

This paper presents the results achieved from microwave radar backscattering measurements of defoliating spruces. Individual spruces were measured in an unechoic chamber and in outdoor conditions and the natural defoliation was simulated by gradually removing the needles of the trees. The measurements were carried out using 5/10 GHz and 35 GHz radar systems. The influence of defoliation to the volume backscattering and extinction coefficient of spruce canopy has been determined from the measured data. The results show that defoliation has a considerable effect on radar backscattering for 10 GHz linear polarizations. At 35 GHz the achieved data indicate a rather complicated and controversial backscattering behaviour with decreasing degree of defoliation. At 5 GHz the effect of defoliation on the backscattering coefficient is negligible. Helicopter-borne measurements of natural defoliation using the 5/10 GHz radar are presented for comparison. Additionally, measurements using a 90 GHz radiometer were conducted. But, by the time of preparing this paper the analysis of these results was not finalised.

Backscattering Behaviour Of Forests At C- And X-band Under Winter Conditions

Helicopter-borne scatterometer measurements of various forest types were conducted on 17 December 1991 in Ruotsinkylii, southern Finland. The scatterometer operates at 5.4 GHz and 9.8 GHz and employs four linear polarizations (W, QH, VH, and HV). At each of the 8 channels, the radar can measure the backscattering properties of a target with a range resolution of 65 cm. The calculated backscattering coefficients of the stands were compared against tree species and forest stand parameter data. Additionally, the effect of incidence angle on the backscattering coefficient was investigated.