Assessment of Antarctic moss health from multi-sensor UAS imagery with Random Forest Modelling

Moss beds are one of very few terrestrial vegetation types that can be found on the Antarctic continent and as such mapping their extent and monitoring their health is important to environmental managers. Across Antarctica, moss beds are experiencing changes in health as their environment changes. As Antarctic moss beds are spatially fragmented with relatively small extent they require very high resolution remotely sensed imagery to monitor their distribution and dynamics. This study demonstrates that multi-sensor imagery collected by an Unmanned Aircraft System (UAS) provides a novel data source for assessment of moss health. In this study, we train a Random Forest Regression Model (RFM) with long-term field quadrats at a study site in the Windmill Islands, East Antarctica and apply it to UAS RGB and 6-band multispectral imagery, derived vegetation indices, 3D topographic data, and thermal imagery to predict moss health. Our results suggest that moss health, expressed as a percentage between 0 and 100% healthy, can be estimated with a root mean squared error (RMSE) between 7 and 12%. The RFM also quantifies the importance of input variables for moss health estimation showing the multispectral sensor data was important for accurate health prediction, such information being essential for planning future field investigations. The RFM was applied to the entire moss bed, providing an extrapolation of the health assessment across a larger spatial area. With further validation the resulting maps could be used for change detection of moss health across multiple sites and seasons

Do daily and seasonal trends in leaf solar induced fluorescence reflect changes in photosynthesis, growth or light exposure?

Solar induced chlorophyll fluorescence (SIF) emissions of photosynthetically active plants retrieved from space-borne observations have been used to improve models of global primary productivity. However, the relationship between SIF and photosynthesis in diurnal and seasonal cycles is still not fully understood, especially at large spatial scales, where direct measurements of photosynthesis are unfeasible. Motivated by up-scaling potential, this study examined the diurnal and seasonal relationship between SIF and photosynthetic parameters measured at the level of individual leaves. We monitored SIF in two plant species, avocado (Persea Americana) and orange jasmine (Murraya paniculatta), throughout 18 diurnal cycles during the Southern Hemisphere spring, summer and autumn, and compared them with simultaneous measurements of photosynthetic yields, and leaf and global irradiances. Results showed that at seasonal time scales SIF is principally correlated with changes in leaf irradiance, electron transport rates (ETR) and constitutive heat dissipation (YNO; p \u3c 0.001). Multiple regression models of correlations between photosynthetic parameters and SIF at diurnal time scales identified leaf irradiance as the principle predictor of SIF (p \u3c 0.001). Previous studies have identified correlations between photosynthetic yields, ETR and SIF at larger spatial scales, where heterogeneous canopy architecture and landscape spatial patterns influence the spectral and photosynthetic measurements. Although this study found a significant correlation between leaf-measured YNO and SIF, future dedicated up-scaling experiments are required to elucidate if these observations are also found at larger spatial scales

Towards remote sensing of vegetation processes

The latest advances in imaging spectroscopy of vegetation enabled remote sensing (RS) of plant reflected or emitted signals associated with photosynthetic processes as the photoprotective transformation of xanthophyll pigments or the chlorophyll fluorescence (Chl-F). A potential future European Space Agency (ESA) satellite mission FLEX is expected to sense, apart from other parameters, so-called steady-state chlorophyll fluorescence (Chl-FS) signal, which may be potentially used for monitoring of photosynthesis (vegetation canopy carbon assimilation rate). Nevertheless, geometric complexity of plant canopies and signal disturbing atmospheric factors require a proper approach for scaling the information of a single leaf optical properties up to the RS image data of anisotropic vegetation canopies. Such up-scaling approach can be established only via synergic measurements of ground based and air-/space-borne optical sensors. Our initial experiment revealed that Chl-FS, being strongly driven by the air temperature, is able to accurately indicate onset and off-set of the photosynthetically active period for the evergreen plants. Next field experiment, carried out with the VNIR imaging spectroradiometer AISA Eagle (SPECIM Ltd., Finland) mounted above the montane grassland and Norway spruce (Picea abies /L./ Karst.) canopies, showed that the fluorescence signal is retrievable from passive optical imaging spectroscopy data. Further analyses revealed that some of the vegetation \u27process-related\u27 optical indices (e.g., photochemical reflectance index - PRI) are closely correlated to the parameters measured over the experimental canopies by eddy-covariance flux systems. The future objective is to continue in development the leaf-canopy Chl-F up-scaling approach by setting up local scale experiments employing the field pocket-size cost effective instruments measuring the leaf optical indices and Chl-F parameters simultaneously with canopy reflectance acquired by RS sensors from tower and aircraft platforms

Imaging spectroscopy of vegetation photosynthetic activity

Abstract of paper that was presented at the Symposium GIS Ostrava 2010: GIS meets Remote Sensing and Photogrammetry towards Digital World, 24-27 Janurary, VSB - Technical University of Ostrava campus, the New Hall building, Ostrava, Czech Republic

Error Budget for Geolocation of Spectroradiometer Point Observations from an Unmanned Aircraft System

We investigate footprint geolocation uncertainties of a spectroradiometer mounted on an unmanned aircraft system (UAS). Two microelectromechanical systems-based inertial measurement units (IMUs) and global navigation satellite system (GNSS) receivers were used to determine the footprint location and extent of the spectroradiometer. Errors originating from the on-board GNSS/IMU sensors were propagated through an aerial data georeferencing model, taking into account a range of values for the spectroradiometer field of view (FOV), integration time, UAS flight speed, above ground level (AGL) flying height, and IMU grade. The spectroradiometer under nominal operating conditions (8 ∘ FOV, 10 m AGL height, 0.6 s integration time, and 3 m/s flying speed) resulted in footprint extent of 140 cm across-track and 320 cm along-track, and a geolocation uncertainty of 11 cm. Flying height and orientation measurement accuracy had the largest influence on the geolocation uncertainty, whereas the FOV, integration time, and flying speed had the biggest impact on the size of the footprint. Furthermore, with an increase in flying height, the rate of increase in geolocation uncertainty was found highest for a low-grade IMU. To increase the footprint geolocation accuracy, we recommend reducing flying height while increasing the FOV which compensates the footprint area loss and increases the signal strength. The disadvantage of a lower flying height and a larger FOV is a higher sensitivity of the footprint size to changing distance from the target. To assist in matching the footprint size to uncertainty ratio with an appropriate spatial scale, we list the expected ratio for a range of IMU grades, FOVs and AGL heights

Using an Unmanned Aerial Vehicle (UAV) to capture micro-topography of Antarctic moss beds

Abstract of the presentation at the Strategic Science in Antarctica: a Joint Australian and New Zealand Conference, 24-26 June 2013, Hobart, Tasmania

Influence of gap fraction on coniferous needle optical properties measurements

Abstract of presentation at the 9th Swiss Geoscience Meeting, Zurich 2011, 11-13 November, ETH Hauptgebaude & Department of Earth Sciences, ETH Zurich

Geometrical and structural parameterization of forest canopy radiative transfer by LIDAR measurements

A forest canopy is a complex system with a highly structural multi-scale architecture. Physical based radiative transfer (RT) modelling has been shown to be an effective tool for retrieval of vegetation canopy biochemical/physical characteristics from optical remote sensing data. A high spatial resolution RT through a forest canopy requires several geometrical and structural parameters of trees and understory to be specified with an appropriate accuracy. Following attributes on forest canopy are required: i) basic tree allometric parameters (i.e., tree height, stem diameter and length, crown length and projection,simplified crown shape, etc.),ii)parameters describing distribution of green biomass (foliage) (e.g., leaf area index (LAI), leaf angle distribution (LAD) or average leaf angle (ALA), clumping of leaves and density of clumps, air gaps and defoliation, etc.), and iii) parameters describing distribution of woody biomass (branches and twigs) (e.g., number, position and angular orientation of the first order branches-branches growing directly from stem, twigarea index (TAI), twig angle distributi on (TAD)). At very high spatial resolution (airborne image data), an insufficiently characterized structure of the forest canopy can result in inaccurate RT simulations. Direct destructive methods of measuring canopy structure are unfeasible at large-scales, therefore, in this paper we review the non-in vasive Light Detection and Ranging (LIDAR) approaches. We also present some results on tree structure parameters acquired by a commercially available ground-based LIDAR scanner employed in scanning the matured Norway spruce trees

Remote monitoring of dynamic canopy photosynthesis with high time resolution light-induced fluorescence transients

Understanding the net photosynthesis of plant canopies requires quantifying photosynthesis in challenging environments, principally due to the variable light intensities and qualities generated by sunlight interactions with clouds and surrounding foliage. The dynamics of sunflecks and rates of change in light intensity at the beginning and end of sustained light (SL) events makes photosynthetic measurements difficult, especially when dealing with less accessible parts of plant foliage. High time resolved photosynthetic monitoring from pulse amplitude modulated (PAM) fluorometers has limited applicability due to the invasive nature of frequently applied saturating flashes. An alternative approach used here provides remote (m), high time resolution (10 s), PAM equivalent but minimally invasive measurements of photosynthetic parameters. We assessed the efficacy of the QA flash protocol from the Light-Induced Fluorescence Transient (LIFT) technique for monitoring photosynthesis in mature outer canopy leaves of potted Persea americana Mill. cv. Haas (Avocado) trees in a semi-controlled environment and outdoors. Initially we established that LIFT measurements were leaf angle independent between ±40° from perpendicular and moreover, that estimates of 685 nm reflectance (R685) from leaves of similar chlorophyll content provide a species dependent, but reasonable proxy for incident light intensity. Photosynthetic responses during brief light events (≤10 min), and the initial stages of SL events, showed similar declines in the quantum yield of photosystem II (ΦII) with large transient increases in \u27constitutive loss processes\u27 (ΦNO) prior to dissipation of excitation by non-photochemical quenching (ΦNPQ). Our results demonstrate the capacity of LIFT to monitor photosynthesis at a distance during highly dynamic light conditions that potentially may improve models of canopy photosynthesis and estimates of plant productivity. For example, generalized additive modelling performed on the 85 dynamic light events monitored identified negative relationships between light event length and ∆ΦII and ∆electron transport rate using either ∆photosynthetically active radiation or ∆R685 as indicators of leaf irradiance

Investigation of Antarctic moss beds using high spatial resolution imaging spectroscopy

Abstract of the presentation at the Strategic Science in Antarctica: a Joint Australian and New Zealand Conference, 24-26 June 2013, Hobart, Tasmania