The use of Microwave Remote Sensing

The engross of micro-cook Remote senseINTRODUCTIONMicrowave conflicting detecting at wavelengths ranging from 1 cm to 1 m has gained a lot of importance over the plast ten-spot for a wide range of scientific performances with the availability of active vaporize radio detection and ranging imaging sy chemical groups. Its dominance in spacial applications use has been scientifically conventional in various sectors same qualityry, agriculture, kill use and land offer, geology and hydrology. A variety of applications dumbfound been carried out world over utilise cook information like discrimination of crop types, crop condition monitor, demesne moisture retrieval, delineation of woodland openings, thought of woodland to a higher place run aground biomass, plant procedure woodwind structure and fire scar mapping, geological mapping, monitor wetlands and snow cover, sea ice denomination, coastal wind depicted object measurement, wave side of meat measuremen t, ship detection , shoreline detection, substrate mapping, slick detection and general botany mapping (Kasischke et al., 1997).There is an emerging interest on microwave external espial is, as microwave sensors it toilet image a ascend with truly fine liquidation of a few meters to coarse resolution of a few kilometers. They rears imagery to a given resolution singly of altitude, limited only by the transmitter power unattached. Fundamental parameters like polarization and look angle apprise be varied to optimize the system for a specific application. SAR imaging is independent of solar blaze as the system provides its own source of illumination. It can operate separately of atmospheric condition conditions if sufficiently long wavelengths argon chosen. It operates in a heap of electromagnetic spectrum contrasting from the good deals employ by visible and infr ard (IR) imageries.Microwave applications in ForestryApplications of microwave channelized(p) feel in woodlandry ha ve likewise been reported during the recent past. Recent reviews on the application of radiolocation in woodsry show that SAR systems have a good potentiality dropity in nifty various types of ( tropic) forest cover use multi-temporal and multi- frequence SAR info (Vander Sanden, 1997 Varekamp, cc1 Quinones, 2002 Sgrenzaroli, 2004). These studies showed that the biomass dependence of radio detection and ranging scatter varies as a function of radio detection and ranging wavelength, polarization and relative incidence angle. Alsorecent studies have demonstrated that synthetic aperture microwave radar (SAR) can be use to label higher up-ground erecting biomass. To date, these studies have relied on capacious ground-truth measurements to construct family relationships between biomass and SAR disperse (Steininger, 1996 Rignot et al., 1997).Many studies demonstrated the use of unreal Aperture radiolocation (SAR) remote sensing to retrieve biophysical characteristics from forest targets (Richards, 1990). Although radar disperse from forest is influenced by their structural properties (Imhoff, 1995), earlier studies derived utilizable relationships between disperseing coefficients and the above-ground biomass (Baker et., 1994 Le Toan et al., 1992 dobsonfly et el., 1992 Imhoff 1995). These relationships whitethorn provide a method of monitoring forest ecosystems which play such(prenominal) a vital theatrical role in light speed storage and NPP.Microwave remote sensing has the ad wagon traintage of all weather capability coverage overcoming the persistent problem of obscure cover in satellite images like in optical information. Optical remote sensing is beingness use very prosperingly in various applications connect to earth resources studies and monitoring of the environment. However, optical remote sensing is not adapted for all atmospheric conditions. It cannot penetrate through clouds and haze. In umteen nations of the world, the buy at cloud conditions often restrain the acquisition of high-quality remotely sensed info by optical sensors. Thus, radar information has become the only operable style of acquiring remotely sensed entropy within a given time frame dissemble because the radar systems can collect universe feature selective information irrespective of weather or light conditions. ascribable to this unique feature of radar selective information compared with optical sensor data, the radar data have been used extensively in many fields, including forest-cover designation and mapping, discrimination of forest compartments and forest types, regard of forest lose parameters and monitoring of forests. In areas where flora cover is dense, it visually covers the underlying formation and it is very difficult to detect structural limiting the use of optical sensors. radiolocation however, is sensitive enough to topographical variation that it is able to discern the structural e xpression reflected in the guide top canopy, and therefore the structure may be clearly defined on the radar imagery.establish on this background, the current thesis work has been carried out to explore the potential of microwave data in addressing core areas of equatorial forestry viz., plant life salmagundi , a bove ground biomass attachment and so on, and to provide the users/researchers a meaningful data foot of SAR applications in tropical forestry, specifically over the India region.Research questionsWhich SAR wavelength/frequency heap is appropriate for vegetation variety in tropical forests?To what extent above ground biomass can be mensurable in tropical forests? Which frequency band and polarization are desirable for above ground biomass love? Is there any enhancement in vegetation classification with polarimetric / interferometric data than stand alone amplitude data?Research hypothesisBased on this background,the previous studies and earlier mentioned Rresearc h questions, we understand that the disperse increases with the increase in above ground biomass and depends on wavelength bands, polarizations used and on the consider area, topographic variations and species composition. So, the present contain attempts to derive the application potential of airborne and quadrangle borne SAR data in the quantification of the forest resources in tropical regions like India, two as a complementary and supplementary role to optical data particularises. several(predicate) techniques such as simple simple regression depth psychology, multi-sensor fusion, texture measures and interferometric coherence characterize contrastive biomass ranges of the test sites and classification of major land cover classes. This study would drive on scope for future research in tropical regions to explore the potentials of SAR data in land cover classification and above ground biomass adhesion use the polarimetric and interferometric techniques. OBJECTIVESBase d on this background, the present study aims at the quest objectivesVegetation type classification utilize polarimetric and interferometric SAR data.Forest above-ground biomass estimation use multi-frequency SAR data and ground inventoried data.Vegetation classification is necessary to understand the innovation of species in a given area which gives above ground biomass with measured parameters. Hence, vegetation classification enhances the estimation of the above ground biomass.Forest biomass is a key parameter in understanding the carbon cycle and ascertain rates of carbon storage, both of which are large uncertainties for forest ecosystems. dead on target knowledge of biophysical parameters of the ecosystems is essential to develop an understanding of the ecosystem and their interactions, to provide input models of ecosystem and global processes, to test these models and to monitor changes in ecosystem dynamics and processes over time. Thus, it is a useful measure for asse ssing changes in forest structure, comparing structural and functional attributes of forest ecosystems across a wide range of environmental conditions.Knowing the spatial distribution of forest biomass is important as the knowledge of biomass is required for compute the sources and sinks of carbon that result from converting a forest to cleared land and delinquency versa, to know the spatial distribution of biomass which enables measurement of change through time. guinea pig sampling is the most followed conventional method for vegetation type classification. The identification of disparate species in field yields good results in the estimation of the above ground biomass. It is very time consuming, expensive and very complicated.With the use of quintuple sensors, varied data collection and interpretation techniques, remote sensing is a versatile tool that can provide data closely the come of the earth to suit any need (Reene et al, 2001). Remote sensing come up for vegetatio n classification is cost effective and alike time effective. though the identification of the guide species is possible only from the aerial imagery, major forest types can be identified from the airborne and the distanceborne remote sensing data. optic image interpretation provides a feasible means of vegetation classification in forests. The image characteristics of shape, size, pattern, shadow, tone and texture are used by interpreters in tree species identification. Phenological correlations are useful in tree species identification. Changes in the appearance of trees in different seasons of the year some times enable discrimination of species that are indistinguishable on single dates. The use of multi-temporal remote sensing data enables the mapping of the different forest types.SAR has shown its potential for screening and monitoring geophysical parameters both locally and globally. Excellent works were carried out on the classification use several approaches such as po larimetric data disintegration (Lee et al., 1998), knowledge establish approaches considering the theoretical backscatter mildew and experimental observations ( Ramson and cold-temperateness , 1994) Backscatter model- link up inversion approaches ( Kurvonen et al., 1999), neural networks and data fusion approaches ( Chen et al., 1996). ring et al. (2001) have shown that the classification accuracy of 95% for the vegetation classes could be achieved through the segmentation and classification of the SAR data using Gaussian Markov Random theatre of operations Model (GMRF).Many methods have been employed for classification of polarimetric SAR data, based on the maximum likelihood (ML) (Lee et al. 1994), artificial neural network (NN) (Chen et al. 1996, Ito and Omatu, 1998), support vector machines (SVMs) (Fukuda et al. 2002), fuzzy method (Chen et al. 2003, Du and Lee 1996), or other approaches (Kong et al. 1988, Lee and Hoppel 1992, van Zyl and Burnette 1992, Cloude and Pottier 1997, Lee et al. 1999, Alberqa 2004) Among these methods, the ML classifier (Lee et al. 1994) can be employed for obtaining faultless classification results, but it is based on the assumption of the complex Wishart distribution of the covariance matrix.Assessing the summarize aboveground biomass of forests (biomass density when expressed as dry weight per whole area at a particular time) is a useful way of quantifying the amount of resource available for all traditional uses. It either gives the step of do biomass directly or the quantity by each parcel (e.g., leaves, branches, and bole) because their biomass tends to vary systematically with the full(a) biomass. However, biomass of each component varies with total biomass by forest type, such as natural or planted forests and closed(a) or open forests. For example, leaves contribute about 3-5% and merchantable bole is about 60% of the total aboveground biomass of closed forests.Many researchers have essential various metho ds based on field inventory and remote sensing approaches for the estimation of above ground biomass (Kira and Ogawa, 1971). Traditionally, field-measured approach is considered as the most accurate source for above-ground biomass estimation. It has been converted to book, or biomass, using allometric equations that are based on standard field measurements (tree height and diameter at depreciator height). contrary approaches, based on field measurement (Brown et al. 1989, Brown and Iverson 1992, Schroeder et al.. 1997, Houghton et al., 2001, Brown, 2002) remote sensing (Tiwari 1994, Roy and Ravan 1996, Tomppo et al., 2002, Foody et al., 2003, Santos et al., 2003, Zheng et al., 2004, Lu, 2005) and GIS (Brown and Gaston 1995) have been applied for AGB estimation. Traditional techniques based on field measurement are the most accurate ways for collecting biomass data. A sufficient number of field measurements is a prerequisite for developing AGB estimation models and for evaluating th e AGB estimation results. However, these approaches are often time consuming, labour intensive, and difficult to implement, particularly in remote areas and are generally limited to 10-year intervals. Also, they cannot provide the spatial distribution of biomass in large areas.For the above reasons, the perspectives of using remote sensing techniques to estimate forest biomass have gained interest. Remote sensing data available at different scales, from local to global, and from various sources, optical to microwave are expected to provide information that could be related indirectly, and in different manners, to biomass information. The possibility that aboveground forest biomass might be determined from space is a promising alternative to ground-based methods (Hese et al., 2005).The usefulnesss of remotely sensed data, such as in repetivity of data collection, synoptic view, digital format that allows fast bear upon of large quantities of data, and the high correlations between spectral bands and vegetation parameters, make it the base source for large area AGB estimation, especially in areas of difficult access. Therefore, remote sensing-based AGB estimation has increasingly attracted scientific interest.In general, AGB can be estimated using remotely sensed data with different approaches, such as octuple regression analysis, K nearest-neighbour, and neural network (Roy and Ravan 1996, Nelson et al. 2000a, Steininger 2000, Foody et al. 2003, Zheng et al. 2004), and indirectly estimated from canopy parameters, such as top out diameter, which are first derived from remotely sensed data using multiple regression analysis or different canopy reflectance models (Wu and Strahler 1994, Woodcock et al. 1997, Phua and Saito 2003, Popescu et al. 2003).Spectral signatures or vegetation indices are often used for AGB estimation in optical remote sensing. Many vegetation indices have been developed and applied to biophysical parameter studies (Anderson and Hanson 1992, Anderson et al. 1993, Eastwood et al. 1997, Lu et al. 2004, Mutanga and Skidmore 2004). Vegetation indices have been recommended to remove variability caused by canopy geometry, soil background, sun view angles, and atmospheric conditions when measuring biophysical properties (Elvidge and Chen 1995, Blackburn and Steele 1999).Radar remote sensing has potential to provide information on above ground biomass. The information content of SAR data in footing of the retrieval of biomass parameters will be assessed based on an understanding of the underlying scattering mechanisms, which in turn are derived from observations and modeling results. For this purpose, an analysis of data acquired by multiple frequency, incidence and polarisation systems and by interferometric systems is carried out. It has been proved that the sensitiveness to biomass parameters differ unbendablely at different frequencies, polarisations and incidence angles.In general, long wavelength SAR backscatter (P and L band) is more sensitive to forest biomass than shorter wavelength C-band backscatter and the relationships saturate at certain biomass levels ( Imhoff 1995b). The strength of the relationships and the saturation levels are dependent on the type of forest being analysed (Ferrazoli et al. 1997). The saturation levels for the estimation of above ground biomass depend on the wavelengths (i.e. different bands, such as C, L, P), polarization (such as HV and VV), and the characteristics of vegetation stand structure and ground conditions. C-band can measure forestry biomass up to app. 50 tons/ha, L-band can measure up to 100 tons/ha and P-band can measure up to 200 tons/ha (Floyd et al., 1998). The combination of multiple channels and polarizations provides greater advantage for estimating total biomass (Harry Stern, 1998).RELEVANCE OF THE STUDYThe present study is the part of Radar resourcefulness satellite Joint Experiment Programme (RISAT-JEP) for forestry applications under taken by Forestry and environmental science Division of National Remote Sensing Centre (NRSC), as a pilot campaign with specific objectives of above ground biomass estimation and vegetation type classification using airborne DLR (German Aerospace Center) carrying ESAR (Experimental semisynthetic Aperture Radar) data for Rajpipla (Gujarat) study site and space borne ENVISAT (Environmental Satellite) carrying advance(a) Synthetic Aperture Radar (ASAR) data for trinity test sites viz., Rajpipla (Gujarat), Dandeli (Karnataka) and Bilaspur (Chattisgarh), India.SCOPE OF THE STUDYThe specific objectives of the present study are above ground biomass estimation and vegetation type classification using airborne DLR (German Aerospace Center) carrying ESAR (Experimental Synthetic Aperture Radar) data for Rajpipla (Gujarat) study site and space borne ENVISAT (Environmental Satellite) carrying Advanced Synthetic Aperture Radar (ASAR) data ALOS (Advanced Land Observing Satellite) carrying Phas ed Array L-band Synthetic Aperture Radar (PALSAR) for three test sites viz., Rajpipla (Gujarat), Dandeli (Karnataka) and Bilaspur (Chattisgarh), India.Different techniques such as Regression analysis, multi-sensor fusion, texture measures and interferometric coherence were used to characterize different biomass ranges of the test sites and to classify the major land cover classes using spaceborne C-band ENVISAT-ASAR data and L-band ALOS- PALSAR data. Polarimetric signatures, polarimetric decompositions, multi-sensor fusion techniques etc. were used for the classification of different vegetation types in the Rajpipla study area using the airborne DLR-ESAR data.The study has its uniqueness and gains importance in the application potential of SAR interferometry over tropical regions like India, both in terms of an alternate/substitute to optical data sets due to persisting cloud cover and to the lack of availability of any earlier scientific work over the study region. This study is us eful for the applications of to be launched Radar Imaging Satellite (RISAT) in 2010.The study has amply demonstrated the application potential of airborne and space borne SAR data in the quantification of the forest resources in tropical regions like India, both as a complementary and supplementary role to optical datasets. The study would facilitate future research in tropical regions to explore the potentials of SAR data in land cover classification and above ground biomass estimation using the polarimetric and interferometric techniques.LITERATURE SURVEYDuring the last decade, many potential applications of SAR in different frequency bands have been studied for forestry applications using data acquired by both airborne and space-borne systems. Various techniques like Polarimetry, Interferometry and Polarimetric-Interferometry intensify the use of SAR data in forestry applications. The backscatter from vegetation is used to generalize information about amplitude data for forest c over mapping and estimation of above ground biomass in regenerate forests. Use of SAR polarimetric data delineated vegetation classes within the forest and also enhanced the capability in estimating the above ground biomass. The use of repeat pass interferometric data enables to calculate the forest stand height and also used for the land cover classification. The emerging Pol-InSAR technique is used to derive the three dimensional forest structures.Forest cover maps were prepared for the boreal, temperate and tropical forests using SAR data. Forest was garbled from non-forest regions using multi-temporal C-band ERS SAR data on the test sites of coupled Kingdom, Poland and Finland (Quegan et al., 2000). The study applied a threshold value to separate forest from other classes. Tropical rainforest of Borneo was mapped from SIR-B data of different incidence angles (Ford and Casey, 1988). Different vegetation covers along with wetlands and clear-cut areas were distinguished. Forest c over mapping was done with JERS-1 SAR data on the coastal regions of Gabon (Simard et al., 2000). The study used decision tree method utilizing both radar amplitude and texture information. Forest cover map was prepared for Southern Chittagong using JERS-1 SAR data (Rahman and Sumantyo, 2007) and the study separated forest, degraded forest, shrubs, coastal plantations, agriculture, shrimp-farms, urban and water.Although radar backscatter from forest is influenced by their structural properties (Imhoff, 1995a), many studies have demonstrated useful relationships between backscattering coefficients and the areal density of above-ground biomass within particular types of forest (Baker et., 1994 Le Toan et al., 1992 Dobson et al., 1992 Imhof et al 1995b).Many airborne and spaceborne SAR systems have been used to carry out a large amount of experiments for investigating the forest ecosystems. The airborne systems, such as the NASA/JPL AIRSAR, DLR-ESAR, etc., operating at P, L and C band, has been flown over many forest sites (Zebker et al., 1991 Le Toan et al, 1992 Beaudoin et al., 1994 Rignot et al. 1994 Skriver et al., 1994 Ranson et al., 1996). The experiments of the Canadian CV-580, as well as the European airborne system, in the first place operating at C and X band also have been carried out in North America and Europe (Drieman et al., 1989 Hoekman, 1990). Spaceborne SAR is being used from regional to global monitoring in a biweekly basis. The spaceborne systems, such as the Seasat SAR, SIR-B, SIR-C/X-SAR and ERS-1, ERS-2, ENVISAT-ASAR, RADARSAT etc., were used for investigations of boreal, temperature and sub-tropical forestry test sites (Ford et al., 1988 Dobson et al., 1992 Ranson et al., 1995 Stofan et al., 1995 Rignotet al., 1995). These experiments and studies have shown that radar is sensitive to forest structural parameters such as diameter at bureau height (dbh) and tree mean height including above-ground biomass (Dobson et al., 1992 Pulliainen et al., 1994 Skriver et al., 1994 Ferrazzoli et al., 1995 Ranson et al., 1996).Earlier studies has shown the potential of radar data in estimating AGB (Hussin et al. 1991, Ranson and Sun 1994, Dobson et al. 1995, Rignot et al. 1995, Saatchi and Moghaddam 1995, Foody et al. 1997, Harrell et al. 1997, Ranson et al. 1997, Luckman et al. 1997, 1998, Pairman et al. 1999, Imhoff et al. 2000, Kuplich et al. 2000, Castel et al. 2002, Sun et al. 2002, Santos et al. 2003, Treuhaft et al. 2004). Kasischke et al. (1997) reviewed radar data for ecological applications, including AGB estimation. Lucas et al. (2004) and Kasischke et al. (2004) reviewed SAR data for AGB estimation in tropical forests and temperate and boreal forests, respectively. Different wavelength radar data have their own characteristics in relating to forest stand parameters. Backscatter in P and L bands is exceedingly correlated with major forest parameters, such as tree age, tree height, DBH, basal area, and AGB (Leckie 1998 ). In particular, SAR L-band data have proven to be invaluable for AGB estimation (Sader 1987, Luckman et al. 1997, Kurvonen et al. 1999, Sun et al. 2002). However, low or negligible correlations were found between SAR C-Band backscatter and AGB (Le Toan et al. 1992). Beaudoin et al. (1994) found that the HH return was related to both trunk and crown biomass, and the VV and HV returns were linked to crown biomass.Harrell et al. (1997) evaluated four techniques for AGB estimation in pine stands using SIR C- and L-Band multi-polarization radar data and found that the L-Band HH polarization data were the critical elements in AGB estimation. Kuplich et al. (2000) used L-band JERS-1/SAR data for AGB estimation of regenerate forests and concluded that these data had the potential to estimate AGB for young, regenerating forests. Sun et al. (2002) found that multi-polarization L-Band SAR data were useful for AGB estimation of forest stands in mountainous areas. Castel et al. (2002) identif ied the significant relationships between the backscatter coefficient of JERS- 1/SAR data and the stand biomass of a pine plantation. The study find the improvement in AGB estimation results for young stands, compared to estimation for old stands. Santos et al. (2002) used JERS-1 SAR data to analyse the relationships between backscatter signals and biomass of forest and savanna formations. This study concluded that forest structural-physiognomic characteristics and the radars volume scattering, double bounce scattering are two important factors affecting these relationships. The saturation levels of backscattering co-efficient with respect to AGB depend on the wavelengths (i.e. different Bands, such as C, L, P), polarization (such as HV and VV), and the characteristics of vegetation stand structure and ground conditions. Luckman et al. (1997) found that the longer-wavelength (L-Band) SAR image was more suitable to tell apart different levels of forest biomass up to a certain thres hold, indicating that it is suitable for estimating biomass of regenerating forests in tropical regions. Austin et al. (2003) indicated that forest biomass estimation using radar data may be feasible when landscape characteristics are taken into account.The radar backscattering coefficient is correlated with forest biomass and stem volume (Le Toan et al. 1992, Israelsson et al. 1994, Kasischke et al. 1994, Dobson et al. 1995). The sensitivity of Synthetic Aperture Radar (SAR) data to forest stem volume increases importantly as the radar wavelength increases (Israelsson et al. 1997). The imaging process makes SAR suitable for mapping parameters related to forest biomass, like stem volume (Baker et al, 1999 Fransson et al, 1999 Hyyppa et al, 1997 Israelsson et al., 1997 Kurvonen et al, 1999 Pulliainen et al, 1996), total growing railway line (Balzter et al, 2000 Schmullius et al, 1997), LAI (Imhoff et al, 1997), or above ground net immemorial productivity (Bergen et al, 1998).Le Toa n et al., (1992) used multi-polarisation L- and P-band airborne radar data, and found that the dynamic range of the radar backscatter corresponded highly with forest growth stages and is maximum at P-band HV polarization. The analysis of P-band data indicated a good correlation between the radar backscatter intensity and the main forest parameters including trunk biomass, height, age, diameter at breast height (dbh), and basal area. Dobson et al., (1992) showed an increasing range of backscatter with ever-changing biomass from C to P-band, as well as higher biomass levels at which backscatter relationships to biomass saturate. Hoekman, (1990) found poor relationships between X- and C-band backscatter and volume and other stand parameters.The spaceborne systems, such as the Seasat SAR, SIR-B, SIR-C/X-SAR and ERS-1, ERS-2, JERS, ENVISAT-ASAR and recently ALOS-PALSAR etc. were used for investigations of boreal, temperature and sub-tropical forestry test sites (Ford et al., 1988 Dobson et al., 1992 Ranson et al., 1995 Stofan et al., 1995 Rignot et al., 1995). These experiments and studies have shown that radar is sensitive to forest structural parameters including above-ground biomass (Dobson et al., 1992 Pulliainen et al., 1994 Skriver et al., 1994 Ferrazzoli et al., 1995 Ranson et al., 1996).Kasischke et al., (1997) reviewed radar data for ecological applications, including AGB estimation. It is being reported in literature that the radar backscatter in the P and L bands is highly correlated with major forest parameters, such as tree age, tree height, DBH, basal area, and AGB. In particular, SAR L-Band data have proven to be valuable for AGB estimation (Sader, 1987 Luckman et al., 1997 Kurvonen et al., 1999 Sun et al., 2002). Kuplich et al., (2000) used JERS-SAR data for AGB estimation of regenerating forests and concluded that these data had the potential to estimate AGB for young, regenerating forests. Luckman et al., (1997) found that the longer-wavelength (L -Band) SAR image was more suitable to discriminate different levels L-Band backscatter shows no sensitivity to increased biomass density after a certain threshold, such as 100 tons ha-1, indicating that it is suitable for estimating biomass of regenerating forests in tropical regions.The radar backscattering coefficient is correlated with forest biomass and stem volume (Le Toan et al. 1992 Israelsson et al., 1994 Kasischke et al., 1994, Dobson et al., 1995). The sensitivity of Synthetic Aperture Radar (SAR) data to forest stem volume increases significantly as the radar wavelength increases (Israelsson et al., 1997). The imaging process makes SAR suitable for mapping parameters related to forest biomass, like stem volume (Baker et al., 1999 Israelsson et al., 1997 Pulliainen et al., 1996), total growing stock (Balzter et al., 2000 Schmullius et al., 1997), LAI (Imhoff et al., 1997), or above ground net primary productivity (Bergen et al., 1998).The dependency of backscatter on above ground biomass was find and related to the penetration of the radiation into the canopy and interaction with the trunk, where most of the volume, therefore, biomass of the vegetation is concentrated (Sader 1987, Le Toan et al. 1992, Dobson et al. 1992). HV polarization in longer wavelengths (L or P band) is the most sensitive to above ground biomass (Sader 1987, Le Toan et al. 1992, Ranson et al. 1997a) because it originates mainly from canopy volume scattering (Wang et al. 1995), trunk scattering (Le Toan et al. 1992) and is less moved(p) by the ground surface (Ranson and Sun 1994).As forest backscatter in different wavelengths and polarizations originate from separate layers of a canopy, the use of multiple channels or multi-step approaches (e.g., Dobson et al. 1995) could be used to estimate total above-ground biomass (Kasischke et al. 1997). Sun and Ranson (1994) estimated biomass in mixed conifer temperate forest upto 250 Mg/ha.Band ratios (HH/HV and VV/VH) were also used fo r the above ground biomass estimation. However, Dobson et al. (1995) considered these band ratios too simplistic (as the corresponding backscatter will be more than higher for the few tall trees than for the many short ones), although effective in estimating biomass at higher ranges. In spite of this, a combination of bands and polarizations in a multi-step approach made possible the mapping of biomass in a mixed temperate forest upto 250 Mg/ha (Dobson et al. 1995). Establishing a strong link between backscatter and forest variables is an important part of the successful estimation of forest biomass from backscatter. Models are often used to explain the relationship between forest variables, scattering mechanisms and SAR configuration parameters (Richards 1990, Kasischke and Christensen 1990). Another approach is the use of statistical analysis, where forest variables are related to SAR backscatter by regression models (Sader 1987, Le Toan et al. 1992, Rauste et al. 1994). The comb ination of the two approaches, in most cases to assess the results of the predicted biomass or backscatter via regression (Ranson and Sun 1994, Ferrazzoli et al. 1997, Franson and Israelson 1999). Statistical procedures such as step-by-step regression analysis were also used to determine the best set of bands and pola