Biomass estimation as a function of vertical forest structure and forest height. Potential and limiations for remote sensing (radar and LiDAR)

Forest biomass stock, spatial distribution and dynamics are unknown parameters for many regions of the world. Today’s information is largely based on ground measurements on a plot basis without coverage in many remote regions that are fundamental for the global carbon cycle. Thus, a method capable of quantifying biomass by means of Remote Sensing (RS) could help to reduce these uncertainties and contribute to a better understanding of it. In this study the capacity to improve the estimation of above-ground biomass (AGB) with a new approach based on forest vertical structure and its potential to improve RS estimations is analyzed. Height to biomass allometry allows biomass estimations from remote sensing systems capable to resolve forest height (LiDAR and polarimetric SAR interferometry (Pol-InSAR)). However, this approach meets its limitations for forest ecosystems under changing conditions in density and structure. To improve biomass estimation accuracy, additional parameters need to be measured. Pol-InSAR and LiDAR allow getting besides forest height vertical backscattering profiles which are connected to forest vertical structure. Thus, due to the relation between structural parameters and AGB expressed by the Structure to Biomass allometry, AGB can be potentially inverted from these systems. The best characterization of forest vertical structure is obtained using the Legendre polynomials. Biomass profiles can be then characterized by the decomposition into a set of Legendre-Fourier basis functions. This method is able to accurately reconstruct vertical biomass profiles with low frequency features. Vertical backscattering profiles are strongly dependent on the sensor used as the resulting profiles are very sensitive to the wavelength and system geometry. E.g. LiDAR profiles are more sensitive to leaves and crowns while Pol-InSAR tends to reconstruct more the woody compartments (stems and branches). In this study, vertical backscattering profiles from short footprint airborne LiDAR and Pol-InSAR data are evaluated for their potential to reconstruct vertical forest structure. With the Legendre decomposition it is possible to parameterize the vertical backscattering profiles and relate them to forest biomass; even though for each remote sensing system different calibration methodologies must be derived. A first step is achieved using the calibration of backscattering signal with known biomass levels showing optimum results. In order to reduce the need of known parameters a new calibration methodology that exploits height to biomass allometric relations has been derived. Inversions using this methodology are tested for LiDAR and SAR profiles showing good correlations for an optimum subset of samples. As each system (frequency) is sensitive to certain biomass components an underestimation is generally expected. Research in this area is ongoing and will be presented with special focus on each system capacity to reconstruct forest vertical biomass distribution for broader sets of samples

Lack of effects of pioglitazone on cardiac function in patients with type 2 diabetes and evidence of left ventricular diastolic dysfunction: a tissue doppler imaging study

<p>Abstract</p> <p>Background</p> <p>Thiazolidinediones, used for the treatment of patients with type 2 diabetes mellitus (DM2), are associated with an increased incidence of heart failure. We sought to investigate the effects of pioglitazone on novel echocardiographic indices of left ventricular (LV) diastolic function in DM2 patients with LV diastolic dysfunction (LVDD).</p> <p>Methods</p> <p>Eighty-eight asymptomatic DM2 patients on metformin and/or sulfonylureas, aged 64.5 ± 7.7 years, without known cardiovascular disease, with normal LV systolic function and evidence of LVDD were randomly assigned to pioglitazone 30 mg/day (n = 42) or an increase in dose of other oral agents (n = 39) for 6 months. All patients underwent transthoracic conventional and Tissue Doppler Imaging echocardiography at baseline and follow-up. The primary end-point was change in early diastolic velocity of the mitral annulus (E').</p> <p>Results</p> <p>Improvement of glycaemic control was similar in the 2 groups. A significant difference (p < 0.05) between the 2 groups was found in the treatment-induced changes in fasting insulin, the insulin resistance index HOMA, HDL cholesterol, triglycerides, diastolic blood pressure (all in favor of pioglitazone) and in body weight (increase with pioglitazone). No significant changes were observed in any echocardiographic parameter in either group and did not differ between groups (p = NS for all). E' increased non-significantly and to a similar extent in both groups (p = NS).</p> <p>Conclusions</p> <p>In asymptomatic DM2 patients with LVDD, the addition of pioglitazone to oral conventional treatment for 6 months does not induce any adverse or favorable changes in LV diastolic or systolic function despite improvements in glycaemic control, insulin sensitivity, lipid profile, and blood pressure.</p

DELTA-K WIDEBAND SAR INTERFEROMETRY FOR DEM GENERATION AND PERSISTENT SCATTERERS USING TERRASAR-X

ABSTRACT Wideband SAR systems such as TerraSAR-X allow estimation of the absolute interferometric phase without resorting to error prone phase unwrapping. This is achieved through the delta-k technique that exploits frequency diversity within the range bandwidth to simulate a SAR system with a much longer carrier wavelength. This benefits all interferometric applications including DEM generation and land surface motion determination. Here we present the results of an ESA study (21318/07/NL/HE) into using delta-k absolute phase estimation for DEM generation and PSI (Persistent Scatterer Interferometry). Using TerraSAR-X data, examples from a delta-k DEM generation system are shown which avoid the errors induced by conventional phase unwrapping. For PSI, the possibilities of absolute phase estimation for a single PS are explored in theory and examples where wideband estimation is compared to conventional PSI processing for a stack of acquisitions over Paris

The European Space Agency BIOMASS mission: Measuring forest above-ground biomass from space

The primary objective of the European Space Agency's 7th Earth Explorer mission, BIOMASS, is to determine the worldwide distribution of forest above-ground biomass (AGB) in order to reduce the major uncertainties in calculations of carbon stocks and fluxes associated with the terrestrial biosphere, including carbon fluxes associated with Land Use Change, forest degradation and forest regrowth. To meet this objective it will carry, for the first time in space, a fully polarimetric P-band synthetic aperture radar (SAR). Three main products will be provided: global maps of both AGB and forest height, with a spatial resolution of 200 m, and maps of severe forest disturbance at 50 m resolution (where “global” is to be understood as subject to Space Object tracking radar restrictions). After launch in 2022, there will be a 3-month commissioning phase, followed by a 14-month phase during which there will be global coverage by SAR tomography. In the succeeding interferometric phase, global polarimetric interferometry Pol-InSAR coverage will be achieved every 7 months up to the end of the 5-year mission. Both Pol-InSAR and TomoSAR will be used to eliminate scattering from the ground (both direct and double bounce backscatter) in forests. In dense tropical forests AGB can then be estimated from the remaining volume scattering using non-linear inversion of a backscattering model. Airborne campaigns in the tropics also indicate that AGB is highly correlated with the backscatter from around 30 m above the ground, as measured by tomography. In contrast, double bounce scattering appears to carry important information about the AGB of boreal forests, so ground cancellation may not be appropriate and the best approach for such forests remains to be finalized. Several methods to exploit these new data in carbon cycle calculations have already been demonstrated. In addition, major mutual gains will be made by combining BIOMASS data with data from other missions that will measure forest biomass, structure, height and change, including the NASA Global Ecosystem Dynamics Investigation lidar deployed on the International Space Station after its launch in December 2018, and the NASA-ISRO NISAR L- and S-band SAR, due for launch in 2022. More generally, space-based measurements of biomass are a core component of a carbon cycle observation and modelling strategy developed by the Group on Earth Observations. Secondary objectives of the mission include imaging of sub-surface geological structures in arid environments, generation of a true Digital Terrain Model without biases caused by forest cover, and measurement of glacier and icesheet velocities. In addition, the operations needed for ionospheric correction of the data will allow very sensitive estimates of ionospheric Total Electron Content and its changes along the dawn-dusk orbit of the mission

A MSFD complementary approach for the assessment of pressures, knowledge and data gaps in Southern European Seas : the PERSEUS experience

PERSEUS project aims to identify the most relevant pressures exerted on the ecosystems of the Southern European Seas (SES), highlighting knowledge and data gaps that endanger the achievement of SES Good Environmental Status (GES) as mandated by the Marine Strategy Framework Directive (MSFD). A complementary approach has been adopted, by a meta-analysis of existing literature on pressure/impact/knowledge gaps summarized in tables related to the MSFD descriptors, discriminating open waters from coastal areas. A comparative assessment of the Initial Assessments (IAs) for five SES countries has been also independently performed. The comparison between meta-analysis results and IAs shows similarities for coastal areas only. Major knowledge gaps have been detected for the biodiversity, marine food web, marine litter and underwater noise descriptors. The meta-analysis also allowed the identification of additional research themes targeting research topics that are requested to the achievement of GES. 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.peer-reviewe

Vertical Resolution Enhancement by Applying Polarimetric Spectral Analysis Techniques to Multibaseline InSAR Data

Polarimetric spectral analysis techniques have been recently introduced for processing multibaseline interferometric synthetic aperture radar data that are affected by the speckle phenomenon. In this paper, their phase estimation accuracy for retrieving the three-dimensional structure of scatterers from measurements corrupted by multiplicative noise is examined. The performance of the polarimetric beamforming, Capon, and MUSIC algorithms is investigated by Monte Carlo simulations and compared with the polarimetric Cramer-Rao bound. It is demonstrated by the CRLB that radar probing systems possessing polarization diversity offer the potential of considerably improving the information extracted from the observation space enlarged by scattering polarimetry. Moreover, it is shown that the polarimetric algorithms lead to noticeably enhanced estimation precision, in particular in terms of refined resolution, under the condition of polarization diversity

Polarimetric Scattering Model for Methane Bubbles Trapped in the Ice of Sub-Artic Lakes

In this work we propose a model for the polarimetric backscattering of shallow sub-arctic lakes, which are frozen usually up to two meters depth during winter. The model takes into account the inhomogeneities in the ice layer introduced mainly by CH4 bubbles trapped in the lake ice. The model is validated against experimental data acquired by ALOS-PalSAR

Polarimetric characterisation of two layered frozen lakes

In terms of radar remote sensing, one of the challenges of future planetary SAR missions will be the estimation of surface, subsurface and upper layer geometric and dielectric characteristics that translate to the localization of subsurface ice and water bodies and could be an indicator for a habitable planet. An example of two-layer structures that appear on earth is frozen lakes. Two layer structures most likely appear in a similar way on other planets as well. For lakes the upper layer consists of ice and the lower one is water. The ice water interface provides high reflectivity for the electromagnetic wave because of the strong dielectric contrast between the two media. Therefore it is a good candidate for evaluating SAR Polarimetric capabilities in subsurface probing. For this L-Band full Polarimetric ALOS(PALSAR) data are used in this research. Previous researches demonstrated the potential of using SAR data for ice monitoring, the growth of ice cover, and freezing to the bottom for shallow Arctic and sub-Arctic lakes in Alaska (Jeffries and Morris, [3]) and northern Canada (Duguay and Lafleur, [2]). The research depends on spatial and temporal variations of the backscattered signal for ice- covered lakes as the mean backscattering from initial ice increases when the ice cover is rather thick for floated ice. Some of the shallow subarctic lakes freeze in winter to the bed forming grounded ice. For those lakes, the mean backscattering from the floated ice decreases as the ice is grounded. With polarimetric observations, frozen lakes can be characterized without the requirement of temporal changes as the polarimetric signature distinguishes clearly ice inhomogeneity influence on the backscattered signal. Further research on modeling the inhomogeneity is required as understanding the influence of different ice structures on the back scattering is essential. [1] Irena Hajnsek: Inversion of Surface Parameters using Polarimetric SAR, Dissertation, DLR Oberpfaffenhofen,(2001). [2] Duguay CR, Pultz TJ, Lafleur PM, Drai D. RADARSAT backscatter characteristics of ice growing on shallow sub-arctic lakes, Churchill, Manitoba, Canada. Hydrological Processes 16: 1631–1644. (2002) [3] Jeffries, M.O., Morris, K. and Kozlenko, N.. Ice characteristics and processes, and remote sensing of frozen rivers and lakes. Remote Sensing in Hydrology, Measuring Environmental Change. Geophysical Monograph 163, C.R. Duguay and A. Pietroniro Editors, American Geophysical Union, Washington, DC. (2005