Remote sensing of sun-induced fluorescence for improved modeling of gross primary productivity in a heterogeneous agricultural area

Gross primary productivity (GPP) is an important parameter to quantify carbon fixation by plant ecosystems. To determine GPP at different spatial scales, remote sensing (RS) offers the unique possibility to provide information from local to global scales. Attempts to estimate GPP from RS data focus on the light-use efficiency (LUE) concept of Monteith that relates GPP to the absorbed photosynthetically active radiation and the efficiency of plant canopies to utilize the absorbed radiation for photosynthesis. To reliably predict GPP at different spatio-temporal scales, LUE has to be linked to optical remote sensing parameters that detect variations in photosynthetic efficiency as a result of changes in environmental conditions. In this study two optical remote sensing parameters were investigated for their potential to serve as a proxy for LUE: the sun-induced fluorescence yield derived from the oxygen absorption O$_{2}$-A band at 760 nm (Fs$_{760}$-yield) and the photochemical reflectance index (PRI). Both parameters were derived from two ASD FieldSpec spectrometers that were operated in parallel, one above the vegetation canopy of either a winter wheat or a sugar beet field and one from a small research aircraft. Based on the LUE concept of Monteith GPP was calculated on a diurnal basis including optical parameters derived from ground observations and compared to simultaneously acquired GPP data from the eddy covariance method. The results showed that the diurnal response of physiological regulation of photosynthesis to changing environmental conditions could be tracked reliably with the Fs$_{760}$-yield or a combination of the Fs760-yield and the PRI. Moreover, the airborne observations were used to characterize the spatial variations of Fs$_{760}$-yield, PRI and GPP of different fields at a regional observation site over the course of a day. Results of this spatio-temporal investigation revealed a significant variability of GPP between different winter wheat fields compared to the within-field variability. For sugar beet the results also showed an increase of the within-field variability in the afternoon in addition to the significant between-field variability. It could be shown that optical RS parameters are sufficiently sensitive to detect a reduction of photosynthetic CO$_{2}$ uptake due to stomatal closure. In the sugar beet canopy this regulation of photosynthesis caused a reduction of GPP in the afternoon ranging from 25 % to 33 % in comparison to maximum GPP values in the morning

User Inquiries and Ground Segment Operation Activities

Since the beginning of the operational phase in November 2022, the Environmental Mapping and Analysis Programm (EnMAP) has gathered substantial interest within the Earth Observation community, counting a considerable number of more than 1800 registered users from over 80 different countries across the globe. The EnMAP data archive is also used very frequently by users with ordering and downloading approx. 2000 tiles per months. Any science user can submit its (his/her) own observations request via the EnMAP Instrument Planning Portal (IPP, https://planning.enmap.org/, also reachable through the official website www.enmap.org), by submitting a proposal. The IP portal also provides access links to the entire EnMAP data archive via the EOWEB Geoportal. The number of users requesting future observations varies significantly based on geographic location. Notably, Europe sees the highest demand for the EnMAP mission, leading to challenges such as conflicting orders for areas within the same orbit. This convergence has introduced complexities in data acquisition, particularly for time series and orchestration of field campaigns. To ensure (increase) regular data acquisition and boost mission efficiency, a "Foreground Mission" has been introduced. This entails prioritized acquisition of extended 990-kilometer flightlines (stripes) over Europe, with a specific focus on Germany. This strategic approach aims to improve data coverage in Germany and streamlines recurring acquisitions along key transects. First this informative presentation provides an assessment of ground segment operations, with special attention given to user feedback and inquiries. Along the way, it outlines the most prevalent user concerns and highlights the strategic factors involved in requesting observations. As second part the audience gains deeper insight into the newly implemented Foreground Mission initiative

The EnMAP imaging spectroscopy mission towards operations

EnMAP (Environmental Mapping and Analysis Program) is a high-resolution imaging spectroscopy remote sensing mission that was successfully launched on April 1st, 2022. Equipped with a prism-based dual-spectrometer, EnMAP performs observations in the spectral range between 418.2 nm and 2445.5 nm with 224 bands and a high radiometric and spectral accuracy and stability. EnMAP products, with a ground instantaneous field-of-view of 30 m x 30 m at a swath width of 30 km, allow for the qualitative and quantitative analysis of surface variables from frequently and consistently acquired observations on a global scale. This article presents the EnMAP mission and details the activities and results of the Launch and Early Orbit and Commissioning Phases until November 1st, 2022. The mission capabilities and expected performances for the operational Routine Phase are provided for existing and future EnMAP users

Sun-Induced Fluorescence as an early indicator for drought stress: a case study in Brazilian soybean varieties

Sun-induced fluorescence (SIF) is a weak signal emitted from the core of the photosystems. It is therefore directly related to stress induced limitations of the photosynthetic efficiency and thus shows a large potential to be an early indicator for plant stress. SIF can be derived in the atmospheric oxygen absorption bands (e.g. O2-A and O2-B bands) using high resolution spectrometers.Within this communication we present the results of a drought stress experiment conducted in Londrina, Brazil. More than four different soybean varieties are grown under water limiting conditions. Previous lab experiments showed different stress resistances of the four varieties to water limiting conditions using state of the art plant physiological and destructive structural measurements.High resolution spectrometers measurements at leaf and close canopy level are used to non-invasively detect drought stress. Classical vegetation reflectance indices and SIF measurements are combined with thermal canopy measurements to detect drought stress in vegetation canopies and to compare the drought stress resistance of the four different soybean varieties.This experiment is a first experiment that will be repeated with different species in the future. In the future improved non-invasive drought stress indicators will be tested by imaging data that are recorded by HyPlant, a novel high performance airborne imaging spectrometer. HyPlant will be used to map SIF by exploiting its high spectral resolution in the window between 670 and 780 nm characterized by a full width at half maximum of 0.26 nm in the atmospheric oxygen absorption bands. In addition, its second module provides data for calculation of reflectance between 400 and 2500 nm

Evaluating the Influence of Plant-Specific Physiological Parameterizationson the Partitioning of Land Surface Energy Fluxes

Plant physiological properties have a significant influence on the partitioning of radiative forcing, the spatial and temporal variability of soil water and soil temperature dynamics, and the rate of carbon fixation. Because of the direct impact on latent heat fluxes, these properties may also influence weather-generating processes, such as the evolution of the atmospheric boundary layer (ABL). In this work, crop-specific physiological characteristics, retrieved from detailed field measurements, are included in the biophysical parameterization of the Terrestrial Systems Modeling Platform (TerrSysMP). The physiological parameters for two typical European midlatitudinal crops (sugar beet and winter wheat) are validated using eddy covariance fluxes over multiple years from three measurement sites located in the North Rhine–Westphalia region of Germany. Comparison with observations and a simulation utilizing the generic crop type shows clear improvements when using the crop-specific physiological characteristics of the plant. In particular, the increase of latent heat fluxes in conjunction with decreased sensible heat fluxes as simulated by the two crops leads to an improved quantification of the diurnal energy partitioning. An independent analysis carried out using estimates of gross primary production reveals that the better agreement between observed and simulated latent heat adopting the plant-specific physiological properties largely stems from an improved simulation of the photosynthesis process. Finally, to evaluate the effects of the crop-specific parameterizations on the ABL dynamics, a series of semi-idealized land–atmosphere coupled simulations is performed by hypothesizing three cropland configurations. These numerical experiments reveal different heat and moisture budgets of the ABL using the crop-specific physiological properties, which clearly impacts the evolution of the boundary layer

A Novel UAV-Based Ultra-Light Weight Spectrometer for Field Spectroscopy

A novel hyperspectral measurement system forunmanned aerial vehicles (UAVs) in the visible to near infrared(VIS/NIR) range (350–800 nm) was developed based on theOcean Optics STS microspectrometer. The ultralight device relieson small open source electronics and weighs a ready-to-fly216 g. The airborne spectrometer is wirelessly synchronized toa second spectrometer on the ground for simultaneous whitereference collection. In this paper, the performance of thesystem is investigated and specific issues such as dark currentcorrection or second order effects are addressed. Full widthat half maximum was between 2.4 and 3.0 nm depending onthe spectral band. The functional system was tested in flightat a 10-m altitude against a current field spectroscopy goldstandard device Analytical Spectral Devices Field Spec 4 overan agricultural site. A highly significant correlation (r2 > 0.99)was found in reflection comparing both measurement approaches.Furthermore, the aerial measurements have a six times smallerstandard deviation than the hand held measurements. Thus, thepresent spectrometer opens a possibility for low-cost but highprecisionfield spectroscopy from UAVs