SRTM DEM accuracy assessment over vegetated areas in Norway

Results from the Shuttle Radar Topography Mission (SRTM) are presented. The SRTM C‐band and X‐band digital elevation models (DEMs) are evaluated with regard to elevation accuracies over agricultural fields, forest areas and man‐made features in Norway. High‐resolution digital maps and satellite images are used as background data. In general, many terrain details can be observed in the SRTM elevation datasets. The elevation accuracy (90% confidence level) of the two SRTM systems is estimated to less than 6.5 m for open agricultural fields and less than 11 m considering all land surface covers. This is better than specifications. Analysis of dense Norwegian forest stands shows that the SRTM system will produce elevation data that are as much as 15 m higher than the ground surface. The SRTM DEM products will therefore partly indicate canopy elevations in forested areas. We also show that SRTM data can be used to update older DEMs obtained from other sources, as well as estimating the volume of rock removed from large man‐made gravel pits.     

Geomorphological changes associated with underground coal mining in the Fushun area,northeast China revealed by multitemporal satellite remote sensing data

Fushun is a famous coal-mining city in northeastern China with more than 100 years of history. Long-term underground coal mining has caused serious surface subsidence in the eastern part of the city. In this study, multitemporal and multisource satellite remote sensing data were used to detect subsidence and geomorphological changes associated with underground coal mining over a 10-year period (1996–2006). A digital elevation model (DEM) was generated through Synthetic Aperture Radar (SAR) interferometry processing using data from a pair of European Remote Sensing Satellite (ERS) SAR images acquired in 1996. In addition, a Shuttle Radar Topography Mission (SRTM) DEM obtained from data in 2000 and an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) DEM from 2006 were used for this study. The multitemporal DEMs indicated that the maximum vertical displacement due to subsidence was around 13 m from 1996 to 2006. Multitemporal ASTER images showed that the flooded water area associated with subsidence had increased by 1.73 km² over the same time period. Field investigations and ground level measurements confirmed that the results obtained from the multitemporal remote sensing data agreed well with ground truth data. This study demonstrates that DEMs derived from multisource satellite remote sensing data can provide a powerful tool to map geomorphological changes associated with underground mining activities.     

DEM‐optical‐radar data integration for palaeohydrological mapping in the northern Darfur,Sudan: implication for groundwater exploration

North‐western Sudan, as a part of the eastern Sahara, is among the driest places on earth. However, the region underwent drastic climatic changes through the alternation of dry and wet conditions in the past. During humid phases, when the rain was plentiful over a prolonged time period, the surface was veined by rivers and dotted by large lakes. The new Shuttle Radar Topography Mission data (SRTM ～90 m) revealed a large endorheic drainage basin, which is centred by a large terminal palaeolake, in the northern Darfur State. The use of GIS methods allowed the delineation of the drainage basin and its associated palaeorivers. The SRTM data along with the Landsat (ETM+) and Radarsat‐1 images corroborate the presence of segments of palaeoshorelines associated with the palaeolake highstands. These constitute a convincing argument of the long‐term existence of a possible pre‐Holocene large water body in the region in the past. The remains of the highest palaeoshoreline have a constant altitude of 573±3 m asl. At its maximum extent, the mega Lake occupied an area of about 30 750 km² (the same size as the Great Bear Lake, Canada's largest lake), which would have contained approximately 2530 km³ of water. This, ancestral lake, which we named the Northern Darfur Megalake (ND Megalake), represents indisputable evidence of the past pluvial conditions in the eastern Sahara. The discovered palaeoshorelines will have significant consequences for improving our knowledge of continental climate change and regional palaeohydorology, and should be taken into consideration in studies of past human habitation in the region. Much of the water carried by the Northern Darfur palaeorivers and the ND Megalake would have percolated into the underlying rocks feeding the Nubian Sandston aquifer. These findings show that the used approach of space‐data integration can help significantly in the groundwater exploration efforts in the Darfur region, where freshwater access is essential for refugee survival, and can be successfully adopted in other parts of Sudan and arid lands in general.     

Book review

This Letter communicates the discovery of an exceptionally large, double‐ringed crater in the eastern part of the Great Sahara, North Africa. The crater is centred at 24.40° N 24.58° E, straddling the boarder between Egypt and Libya. It is the 15th and largest impact crater identified in the Sahara. Landsat Enhanced Thematic Mapper Plus (ETM+) images as well as Radarsat‐1 data reveal a discontinuous outer rim, 31 km in diameter, and a group of prominences forming an inner ring. The Nubian sandstone surface in which the crater was formed has undergone severe erosion. Thus, the crater morphology was affected by both aeolian and fluvial processes. Courses of a major river and smaller streams, now dry, have eroded much of the crater's outer rim as revealed by Shuttle Radar Topography Mission (SRTM) data. The probable impact that created the crater, named Kebira, meaning large in Arabic, is possibly the source of the silica glass fragments that abound on the desert surface between giant linear dunes of the Great Sand Sea in southwestern Egypt.     

利用星载InSAR技术提取镇江地区DEM及其精度分析

InSAR技术是目前获取高精度数字高程模型（DEM）的一种新方法。为了分析InSAR技术提取DEM的精度,首先介绍了美国航天飞机雷达SRTM DEM的精度和数据结构,然后以江苏镇江地区作为试验区,采用ERS1/2卫星影像来提取DEM,并对星载SAR提取的DEM与SRTM 3弧秒分辨率DEM的精度作了比较。 结果表明,利用星载SAR提取的DEM分辨率与SRTM 3弧秒分辨率的DEM相当,能很好地显示出地形起伏（如山脉、沟谷）的纹理特征。进一步的研究还表明,利用InSAR技术提取DEM的精度与SRTM 3 DEM之间存在5米左右的系统误差,并对产生这一系统误差的原因作了详细分析。     

Validation of surface height from shuttle radar topography mission using shuttle laser altimeter

Spaceborne Interferometric SAR (InSAR) technology used in the Shuttle Radar Topography Mission (SRTM) and spaceborne lidar such as Shuttle Laser Altimeter-02 (SLA-02) are two promising technologies for providing global scale digital elevation models (DEMs). Each type of these systems has limitations that affect the accuracy or extent of coverage. These systems are complementary in developing DEM data. In this study, surface height measured independently by SRTM and SLA-02 was cross-validated. SLA data was first verified by field observations, and examinations of individual lidar waveforms. The geolocation accuracy of the SLA height data sets was examined by checking the correlation between the SLA surface height with SRTM height at 90 m resolution, while shifting the SLA ground track within its specified horizontal errors. It was found that the heights from the two instruments were highly correlated along the SLA ground track, and shifting the positions did not improve the correlation significantly. Absolute surface heights from SRTM and SLA referenced to the same horizontal and vertical datum (World Geodetic System (WGS) 84 Ellipsoid) were compared. The effects of forest cover and surface slope on the height difference were also examined. After removing the forest effect on SRTM height, the mean height difference with SLA-02 was near zero. It can be further inferred from the standard deviation of the height differences that the absolute accuracy of SRTM height at low vegetation area is better than the SRTM mission specifications (16 m). The SRTM height bias caused by forest cover needs to be further examined using future spaceborne lidar (e.g. GLAS) data.     

Digital terrain analysis using Landsat‐7 ETM+ imagery and SRTM DEM: a case study of Nevsehir province (Cappadocia), Turkey

A three‐dimensional (3D) model of land‐use/land‐cover (LULC) and a digital terrain model of Nevsehir province (Cappadocia), Turkey, were generated and analysed using a Landsat‐7 Enhanced Thematic Mapper Plus (ETM+) multispectral image set and a Shuttle Radar Topographic Mission (SRTM) digital elevation model (DEM). Stream drainage patterns, lineaments and structural‐geological features (landforms) were extracted and analysed. In the process of analysing and interpreting the multispectral images of geological features, criteria such as colour and colour tones, topography and stream drainage patterns were used to acquire information about the geological structures of the land, including as geomorphological, topographic and tectonic structures. Landsat‐7 ETM+ multispectral imagery and an SRTM DEM of the study region were used experimentally for classification and analysis of a digital terrain model. Using the multispectral image data, the LULC types were classified as: settlement (1.2%); agricultural land (70.1%); forest (scrubland, orchard and grassland) (2.9%); bare ground (25.5%); and water bodies (lakes and rivers) (0.3%) of the study area (5434 km²). The results of the DEM classification in the study area were: river flood plain (11.3%); plateau (52.3%); high plateau (28.4%); mountain (7.6%); and high mountain (0.3%). Lineament analysis revealed that the central Kizilirmak River divides the region into two nearly equal parts: the Kirsehir Plateau in the north and the Nevsehir Plateau in the south. In terms of the danger of catastrophe, the settlements of Kozakli, Hacibektas and Acigol were found to be at less risk of earthquake and/or flooding than those of Avanos, Gulsehir, Urgup, Nevsehir, Gumuskent and Derinkuyu, which are located on river flood plains and/or the main stream drainage channels, particularly stream beds, where the lineaments are deep valleys or fracture or fault‐line indicators.     

SRTM vs ASTER elevation products. Comparison for two regions in Crete,Greece

The Shuttle Radar Topography Mission (SRTM) collected elevation data over 80% of earth's land area during an 11‐day Space Shuttle mission. With a horizontal resolution of 3 arc sec, SRTM represents the best quality, freely available digital elevation models (DEMs) worldwide. Since the SRTM elevation data are unedited, they contain occasional voids, or gaps, where the terrain lay in the radar beam's shadow or in areas of extremely low radar backscatter, such as sea, dams, lakes and virtually any water‐covered surface. In contrast to the short duration of the SRTM mission, the ongoing Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is continuously collecting elevation information with a horizontal resolution of 15 m. In this paper we compared DEM products created from SRTM data with respective products created from ASTER stereo‐pairs. The study areas were located in Crete, Greece. Absolute DEMs produced photogrammetricaly from ASTER using differentially corrected GPS measurements provided the benchmark to infer vertical and planimetric accuracy of the 3 arc sec finished SRTM product. Spatial filters were used to detect and remove the voids, as well as to interpolate the missing values in DEMs. Comparison between SRTM‐ and ASTER‐derived DEMs allowed a qualitative assessment of the horizontal and vertical component of the error, while statistical measures were used to estimate their vertical accuracy. Elevation difference between SRTM and ASTER products was evaluated using the root mean square error (RMSE), which was found to be less than 50 m.     

Filling voids of SRTM with Landsat sensor imagery in rugged terrain

The Shuttle Radar Topography Mission (SRTM) delivered a free digital elevation model (DEM) with a spatial resolution of 3″ at near global coverage. However, there are many data voids in the SRTM data that need to be filled before their application. In this Letter, a novel void‐filling method, which uses Landsat sensor imagery to provide detailed information on terrains for the filling procedure, is proposed. Valleys are extracted from Landsat sensor imagery first, then elevation values of SRTM voids along valleys are interpolated, and finally the remaining voids are patched with the global coarse resolution DEM. The test results show that the elevation values filled with the proposed method perform better than those filled with the traditional method and local geomorphological features can be maintained with the proposed method.     

Estimating vertical error of SRTM and map-based DEMs using ICESat altimetry data in the eastern Tibetan Plateau

The Geoscience Laser Altimeter System (GLAS) instrument onboard the Ice, Cloud and land Elevation Satellite (ICESat) provides elevation data with very high accuracy which can be used as ground data to evaluate the vertical accuracy of an existing Digital Elevation Model (DEM). In this article, we examine the differences between ICESat elevation data (from the 1064 nm channel) and Shuttle Radar Topography Mission (SRTM) DEM of 3 arcsec resolution (90 m) and map-based DEMs in the Qinghai-Tibet (or Tibetan) Plateau, China. Both DEMs are linearly correlated with ICESat elevation for different land covers and the SRTM DEM shows a stronger correlation with ICESat elevations than the map-based DEM on all land-cover types. The statistics indicate that land cover, surface slope and roughness influence the vertical accuracy of the two DEMs. The standard deviation of the elevation differences between the two DEMs and the ICESat elevation gradually increases as the vegetation stands, terrain slope or surface roughness increase. The SRTM DEM consistently shows a smaller vertical error than the map-based DEM. The overall means and standard deviations of the elevation differences between ICESat and SRTM DEM and between ICESat and the map-based DEM over the study area are 1.03 ± 15.20 and 4.58 ± 26.01 m, respectively. Our results suggest that the SRTM DEM has a higher accuracy than the map-based DEM of the region. It is found that ICESat elevation increases when snow is falling and decreases during snow or glacier melting, while the SRTM DEM gives a relative stable elevation of the snow/land interface or a glacier elevation where the C-band can penetrate through or reach it. Therefore, this makes the SRTM DEM a promising dataset (baseline) for monitoring glacier volume change since 2000.     

Remote sensing and GIS applications of surface and near-surface hydromorphological features in Darfur region,Sudan

Groundwater modelling and mapping in a region partly inaccessible using traditional techniques is practically very difficult, and time and cost consuming. However, integration of remote sensing and GIS enables more reliable mapping and analysis of hydromorphological elements such as palaeolakes. In the present study, a set of automated morphometric techniques of fitting a bivariate quadratic surface in a moving window of size 3 × 3 was used and modified to map and analyse hydromorphological elements in northwestern Sudan. Geomorphometry results indicate that the palaeodrainage network incision and depressions may have received most of the rainwater during late Quaternary wet phases. The results revealed that of the total 2000 km² coverage of the unnamed depression, about 49.6% was classified as accumulation zone with a recharge area of about 992 km², while the Wadi Fesh Fesh and Oyo depressions were shown to have the smallest areas of accumulation zone, approximately 31.3% and 37.3%, respectively. Validation of the methods was made by comparing trends and textural features from a Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) with 30 m spatial resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) DEM and 0.6 m spatial resolution Quickbird images and geological maps of the study area. The maps obtained showed a strong correlation, indicating that the proposed methods are very efficient tools for regional mapping and analysing hydromorphological elements in arid regions and remote and inaccessible regions.     

SRTM 3″ DEM (versions 1, 2, 3, 4) validation by means of extensive kinematic GPS measurements: a case study from North Greece

In 2000, the Shuttle Radar Topography Mission (SRTM) provided for the first time a global high-quality digital elevation model (DEM) at resolution levels of one and three arcseconds, using single-pass synthetic aperture radar (SAR) interferometry. In January and February 2008, an extensive four-day kinematic global positioning system (GPS) (KGPS) campaign was carried out in the vicinity of the city of Thessaloniki (North Greece), during which more than 60 000 points were collected, providing an unprecedented density of measurements in the order of 20 points km^?2. The purpose of the present study was to assess the vertical accuracy of the four versions of SRTM 3″ DEMs that are currently available over the Internet for public use, on the basis of the KGPS data collected.     

Calibration and validation of a set of multi‐aspect airborne polarimetric Pi‐SAR data

To implement target reconstruction from multi‐aspect SAR data, a simple method of first calibrating multi‐aspect data is presented. It requires that at least one aspect is calibrated beforehand, and other aspects are then calibrated with respect to this calibrated aspect. A natural object, such as flat bare ground, is usually chosen as a reference target, and is expected to preserve identical scattering for all aspects. Thereafter, the channel imbalance factors are estimated from the distribution of the phase difference and amplitude ratio of co‐polarized, hh and vv, echoes of the reference target, and are then used to compensate the whole SAR images. This approach was applied to the calibration of four‐aspect airborne Pi‐SAR (Polarimetric and Interferometric Synthetic Aperture Radar) data for target reconstruction. Based on the same principle, another potential application is calibration of descending (ascending) data using the calibrated ascending (descending) data.     

Geomorphometric features and tectonic activities in sub-Himalayan thrust belt,Pakistan, from satellite data

The sub-Himalayan thrust belt is an active thrust wedge which progresses southward over the north-dipping Indian plate. The north–south compression resulted in severe deformation of sedimentary rocks in this belt. Distinct thrust geometries and topography have evolved under the interaction between tectonic and erosional environments. To better understand the relationship between tectonics and topography, A Digital Elevation Model (DEM) derived from Shuttle Radar Topography Mission (SRTM) data was used to extract the geomorphic and drainage features. Based on comprehensive analyses of topographic relief, drainage density, and drainage patterns, nine topographic units were identified. The thrust wedge was divided into three physiographic assemblages with apparent lateral variations. These units match up with the interpreted main structures from the Landsat Enhanced Thematic Mapper Plus (ETM+) images and published geological maps. The relationship between geomorphometric features and tectonics indicates that structural activities primarily control the topography in the sub-Himalayan thrust belt. Topographic features are indicative of tectonics in the young tectonic regions with low elevation.     

Extracting digital elevation models from SAR data through independent component analysis

This article illustrates findings about a new method for the extraction of digital elevation model (DEM) from interferograms of synthetic aperture radar (SAR) data, based on independent component analysis (ICA). This method is named InSAR-ICA, and its advantages are related to its capability in estimating topographical altitudes without taking into account any or sparse non-SAR data (e.g. ground-based or atmospheric parameters). This is especially useful in cases of mountainous regions, where large altitude changes over short distances and the presence of microclimates generally limit the possibility of DEM estimates by few SAR interferograms only. A comparison between the standard SRTM (Shuttle Radar Topographical Mission) elevations and those extracted by InSAR-ICA is carried out for the region of South Italy, Apennine Mountains. Results are interpreted in terms of the reliability of InSAR-ICA DEM estimates.     

Mapping vegetation in a late Quaternary landform of the Amazonian wetlands using object-based image analysis and decision tree classification

Fan-shaped morphologies related to late Quaternary residual megafan depositional systems are common features over wide areas in northern Amazonia. These features were formed by ancient distributary drainage systems that are in great contrast to tributary drainage networks that typify the modern Amazon basin. The surfaces of the Amazonian megafans constitute vegetacional mosaic wetlands with different campinarana types. A fine-scale-resolution investigation is required to provide detailed classification maps for the various campinarana and surrounding forest types associated with the Amazonian megafans. This approach remains to be presented, despite its relevance for analysing the relationship between stages of plant succession and sedimentary dynamics associated with the evolution of megafans. In this work, we develop a methodology for classifying vegetation over a fan-shaped megafan palaeoform from a northern Amazonian wetland. The approach included object-based image analysis (OBIA) and data-mining (DM) techniques combining Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images, land-cover fractions derived by the linear spectral mixing model, synthetic aperture radar (SAR) images, and the digital elevation model (DEM) acquired during the Shuttle Radar Topography Mission (SRTM). The DEM, vegetation fraction, and ASTER band 3 were the most useful parameters for defining the forest classes. The normalized difference vegetation index (NDVI), ASTER band 1, vegetation fraction, and the Advanced Land Observing Satellite (ALOS)/Phased Array type L-band Synthetic Aperture Radar (PALSAR) transmitting and receiving horizontal polarization (HH) and transmitting horizontal and receiving vertical polarization (HV) were all effective in distinguishing the wetland classes campinarana and Mauritia. Tests of statistical significance indicated the overall accuracies and kappa coefficients (κ) of 88% and 0.86 for the final map, respectively. The allocation disagreement coefficient of 5% and a quantity disagreement value of 7% further attested the statistical significance of the classification results. Hence, in addition to water, exposed soil, and deforestation areas, OBIA and DM were successful for differentiating a large number of open (forest, wood, shrub, and grass campinaranas), forest (terra firme, várzea, igapó, and alluvial), as well as Mauritia wetland classes in the inner and outer areas of the studied megafan.     

Geo-referencing of continental-scale JERS-1 SAR mosaics based on matching homologous features with a digital elevation model: theory and practice

An effective method for a posteriori ortho-rectification of continental-scale synthetic aperture radar (SAR) mosaics using a digital elevation model (DEM) has been developed. The method is based on homologous feature matching between the DEM and a simulated SAR image. The simulated image is derived from the radar-viewing geometry, topographic information and contextual information provided by the Shuttle Radar Topography Mission (SRTM), shorelines and water bodies database (SWBD) and GeoCover Landsat mosaics. Two large L-band SAR mosaics (the global boreal forest mapping (GBFM) Siberia mosaic and the global rain forest mapping (GRFM) Africa mosaic), assembled from the Japanese Earth Resources Satellite-1 (JERS-1) data, were accurately geo-referenced and ortho-rectified. The GRFM Africa mosaic was also radiometrically corrected for topographic effects. The accurate co-registration with the DEM allows for improved classification methods based on the combination of SAR backscatter with terrain features. Comparison of the revised GBFM and GRFM mosaics with a forthcoming set of continental-scale mosaics assembled from the Advanced Land Observing Satellite (ALOS) Phased Array L-band Synthetic Aperture Radar (PALSAR) data will offer a unique possibility for change detection studies over the Tropical and Boreal forest zones with a temporal spacing of some 10 years.     

Semi‐automated methods for mapping wetlands using Landsat ETM+ and SRTM data

The overarching goal of this study was to develop a comprehensive methodology for mapping natural and human‐made wetlands using fine resolution Landsat enhanced thematic mapper plus (ETM+), space shuttle radar topographic mission digital elevation model (SRTM DEM) data and secondary data. First, automated methods were investigated in order to rapidly delineate wetlands; this involved using: (a) algorithms on SRTM DEM data, (b) thresholds of SRTM‐derived slopes, (c) thresholds of ETM+ spectral indices and wavebands and (d) automated classification techniques using ETM+ data. These algorithms and thresholds using SRTM DEM data either over‐estimated or under‐estimated stream densities (S _d) and stream frequencies (S _f), often generating spurious (non‐existent) streams and/or, at many times, providing glaring inconsistencies in the precise physical location of the streams. The best of the ETM+‐derived indices and wavebands either had low overall mapping accuracies and/or high levels of errors of omissions and/or errors of commissions.

Second, given the failure of automated approaches, semi‐automated approaches were investigated; this involved the: (a) enhancement of images through ratios to highlight wetlands from non‐wetlands, (b) display of enhanced images in red, green, blue (RGB) false colour composites (FCCs) to highlight wetland boundaries, (c) digitizing the enhanced and displayed images to delineate wetlands from non‐wetlands and (d) classification of the delineated wetland areas into various wetland classes. The best FCC RGB displays of ETM+ bands for separating wetlands from other land units were: (a) ETM+4/ETM+7, ETM+4/ETM+3, ETM+4/ETM+2, (b) ETM+4, ETM+3, ETM+5 and (c) ETM+3, ETM+2, ETM+1. In addition, the SRTM slope threshold of less than 1% was very useful in delineating higher‐order wetland boundaries. The wetlands were delineated using the semi‐automated methods with an accuracy of 96% as determined using field‐plot data.

The methodology was evaluated for the Ruhuna river basin in Sri Lanka, which has a diverse landscape ranging from sea shore to hilly areas, low to very steep slopes (0° to 50°), arid to semi‐arid zones and rain fed to irrigated lands. Twenty‐four per cent (145 733 ha) of the total basin area was wetlands as a result of a high proportion of human‐made irrigated areas, mainly under rice cropping. The wetland classes consisted of irrigated areas, lagoons, mangroves, natural vegetation, permanent marshes, salt pans, lagoons, seasonal wetlands and water bodies. The overall accuracies of wetland classes varied between 87% and 94% (K _hat = 0.83 to 0.92) with errors of omission less than 13% and errors of commission less than 1%.     

Vegetation height estimation from Shuttle Radar Topography Mission and National Elevation Datasets

A study was conducted to determine the feasibility of obtaining estimates of vegetation canopy height from digital elevation data collected during the 2000 Shuttle Radar Topography Mission (SRTM). The SRTM sensor mapped 80% of the Earth's land mass with a C-band Interferometric Synthetic Aperture Radar (InSAR) instrument, producing the most complete digital surface map of Earth. Due to the relatively short wavelength (5.6 cm) of the SRTM instrument, the majority of incoming electromagnetic energy is reflected by scatterers located within the vegetation canopy at heights well above the “bald-Earth” surface. Interferometric SAR theory provides a basis for properly identifying and accounting for the dependence of this scattering phase center height on both instrument and target characteristics, including relative and absolute vertical error and vegetation structural attributes.An investigation to quantify the magnitude of the vertical error component was conducted using SRTM data from two vegetation-free areas in Iowa and North Dakota, revealing absolute errors of −4.0 and −1.1 m, respectively. It was also shown that the relative vertical error due to phase noise can be reduced significantly through sample averaging. The relative error range for the Iowa site was reduced from 13 to 4 m and for the North Dakota site from 7 to 3 m after averaging of 50 samples. Following error reduction, it was demonstrated that the SRTM elevation data can be successfully correlated via linear regression models with ground-measured canopy heights acquired during the general mission timeframe from test sites located in Georgia and California. Prior to outlier removal and phase noise reduction, initial adjusted r² values for the Georgia and California sites were 0.15 and 0.20, respectively. Following outlier analysis and averaging of at least 20 SRTM pixels per observation, adjusted r² values for the Georgia and California sites improved to 0.79 (rmse=1.1 m) and 0.75 (rmse=4.5 m), respectively. An independent validation of a novel bin-based modeling strategy designed for reducing phase noise in sample plot data confirmed both the robustness of the California model (adjusted r²=0.74) as well as the capacity of the binning strategy to produce stable models suitable for inversion (validated rmse=4.1 m). The results suggest that a minimum mapping unit of approximately 1.8 ha is appropriate for SRTM-based vegetation canopy height mapping.     

A multi-sensor approach for mapping plant-derived carbon storage in Amazonian podzols

The Rio Negro basin is characterized by the extensive occurrence of podzol-type soils that store large amounts of organic matter in depth, resulting in the storage of carbon able available to the atmosphere with climate change. The quantification of this carbon requires determination of podzol types and their spatial distribution. Remote-sensing techniques would be helpful in indirect spatializing and segmentation of soil groups in Amazonian podzols. Here we associated remote-sensing images (Shuttle Radar Topographic Mission (SRTM), Operational Land Imager sensor/Landsat 8, and Thermal Infrared Sensor/Landsat 8) and field sample data in order to achieve carbon stock mapping. We found that a multi-sensor approach was critical for a proper segmentation of vegetation groups and spatial distribution of areas with different hydrologic soil regimes.