Potential of the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor for the monitoring of terrestrial chlorophyll fluorescence

Global monitoring of sun-induced chlorophyll fluorescence (SIF) is improving our knowledge about the photosynthetic functioning of terrestrial ecosystems. The feasibility of SIF retrievals from spaceborne atmospheric spectrometers has been demonstrated by a number of studies in the last years. In this work, we investigate the potential of the upcoming TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor satellite mission for SIF retrieval. TROPOMI will sample the 675–775 nm spectral window with a spectral resolution of 0.5 nm and a pixel size of 7 km × 7 km. We use an extensive set of simulated TROPOMI data in order to assess the uncertainty of single SIF retrievals and subsequent spatio-temporal composites. Our results illustrate the enormous improvement in SIF monitoring achievable with TROPOMI with respect to comparable spectrometers currently in-flight, such as the Global Ozone Monitoring Experiment-2 (GOME-2) instrument. We find that TROPOMI can reduce global uncertainties in SIF mapping by more than a factor of 2 with respect to GOME-2, which comes together with an approximately 5-fold improvement in spatial sampling. Finally, we discuss the potential of TROPOMI to map other important vegetation parameters at a global scale with moderate spatial resolution and short revisit time. Those include leaf photosynthetic pigments and proxies for canopy structure, which will complement SIF retrievals for a self-contained description of vegetation condition and functioning

MODIS: Moderate Resolution Imaging Spectrometer

This brochure describes the Moderate Resolution Imaging Spectrometer (MODIS) instrument on NASA's Terra satellite. The first NASA Earth Observing System (EOS) satellite, Terra, was launched on December 18, 1999, carrying five remote sensors. The most comprehensive EOS sensor is MODIS which offers a unique combination of features: it detects a wide spectral range of electromagnetic energy; it takes measurements at three spatial resolutions (levels of detail); it takes measurements all day, every day; and it has a wide field of view. This continual, comprehensive coverage allows MODIS to complete an electromagnetic picture of the globe every two days. Educational levels: Undergraduate lower division, Undergraduate upper division, Graduate or professional, Informal education

Quantitative estimation of vegetation traits and temporal dynamics using 3-D radiative transfer models, high-resolution hyperspectral images and satellite imagery

Large-scale monitoring of vegetation dynamics by remote sensing is key to detecting early signs of vegetation decline. Spectral-based indicators of phys-iological plant traits (PTs) have the potential to quantify variations in pho-tosynthetic pigments, chlorophyll fluorescence emission, and structural changes of vegetation as a function of stress. However, the specific response of PTs to disease-induced decline in heterogeneous canopies remains largely unknown, which is critical for the early detection of irreversible damage at different scales. Four specific objectives were defined in this research: i) to assess the feasibility of modelling the incidence and severity of Phytophthora cinnamomi and Xylella fastidiosa based on PTs and biophysical properties of vegetation; ii) to assess non-visual early indicators, iii) to retrieve PT using radiative transfer models (RTM), high-resolution imagery and satellite observations; and iv) to establish the basis for scaling up PTs at different spatial resolutions using RTM for their retrieval in different vegetation co-vers. This thesis integrates different approaches combining field data, air- and space-borne imagery, and physical and empirical models that allow the retrieval of indicators and the evaluation of each component’s contribution to understanding temporal variations of disease-induced symptoms in heter-ogeneous canopies. Furthermore, the effects associated with the understory are introduced, showing not only their impact but also providing a compre-hensive model to account for it. Consequently, a new methodology has been established to detect vegetation health processes and the influence of biotic and abiotic factors, considering different components of the canopy and their impact on the aggregated signal. It is expected that, using the presented methods, existing remote sensors and future developments, the ability to detect and assess vegetation health globally will have a substantial impact not only on socio-economic factors, but also on the preservation of our eco-system as a whole

Scientific and technical challenges in remote sensing of plant canopy reflectance and fluorescence

State-of-the-art optical remote sensing of vegetation canopies is reviewed here to stimulate support from laboratory and field plant research. This overview of recent satellite spectral sensors and the methods used to retrieve remotely quantitative biophysical and biochemical characteristics of vegetation canopies shows that there have been substantial advances in optical remote sensing over the past few decades. Nevertheless, adaptation and transfer of currently available fluorometric methods aboard air- and space-borne platforms can help to eliminate errors and uncertainties in recent remote sensing data interpretation. With this perspective, red and blue-green fluorescence emission as measured in the laboratory and field is reviewed. Remotely sensed plant fluorescence signals have the potential to facilitate a better understanding of vegetation photosynthetic dynamics and primary production on a large scale. The review summarizes several scientific challenges that still need to be resolved to achieve operational fluorescence based remote sensing approache

Potential of the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor for the monitoring of terrestrial chlorophyll fluorescence

Global monitoring of sun-induced chlorophyll fluorescence (SIF) is improving our knowledge about the photosynthetic functioning of terrestrial ecosystems. The feasibility of SIF retrievals from spaceborne atmospheric spectrometers has been demonstrated by a number of studies in the last years. In this work, we investigate the potential of the upcoming TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor satellite mission for SIF retrieval. TROPOMI will sample the 675–775 nm spectral window with a spectral resolution of 0.5 nm and a pixel size of 7 km × 7 km. We use an extensive set of simulated TROPOMI data in order to assess the uncertainty of single SIF retrievals and subsequent spatio-temporal composites. Our results illustrate the enormous improvement in SIF monitoring achievable with TROPOMI with respect to comparable spectrometers currently in-flight, such as the Global Ozone Monitoring Experiment-2 (GOME-2) instrument. We find that TROPOMI can reduce global uncertainties in SIF mapping by more than a factor of 2 with respect to GOME-2, which comes together with an approximately 5-fold improvement in spatial sampling. Finally, we discuss the potential of TROPOMI to map other important vegetation parameters at a global scale with moderate spatial resolution and short revisit time. Those include leaf photosynthetic pigments and proxies for canopy structure, which will complement SIF retrievals for a self-contained description of vegetation condition and functioning

Assessing the contribution of understory sun-induced chlorophyll fluorescence through 3-D radiative transfer modelling and field data

A major international effort has been made to monitor sun-induced chlorophyll fluorescence (SIF) from space as a proxy for the photosynthetic activity of terrestrial vegetation. However, the effect of spatial heterogeneity on the SIF retrievals from canopy radiance derived from images with medium and low spatial resolution remains uncharacterised. In images from forest and agricultural landscapes, the background comprises a mixture of soil and understory and can generate confounding effects that limit the interpretation of the SIF at the canopy level. This paper aims to improve the understanding of SIF from coarse spatial resolutions in heterogeneous canopies by considering the separated contribution of tree crowns, understory and background components, using a modified version of the FluorFLIGHT radiative transfer model (RTM). The new model is compared with others through the RAMI model intercomparison framework and is validated with airborne data. The airborne campaign includes high-resolution data collected over a tree-grass ecosystem with the HyPlant imaging spectrometer within the FLuorescence EXplorer (FLEX) preparatory missions. Field data measurements were collected from plots with a varying fraction of tree and understory vegetation cover. The relationship between airborne SIF calculated from pure tree crowns and aggregated pixels shows the effect of the understory at different resolutions. For a pixel size smaller than the mean crown size, the impact of the background was low (R2 > 0.99; NRMSE 0.2). This study demonstrates that using a 3D RTM model improves the calculation of SIF significantly (R2 = 0.83, RMSE = 0.03 mW m−2 sr−1 nm−1) when the specific contribution of the soil and understory layers are accounted for, in comparison with the SIF calculated from mixed pixels that considers only one layer as background (R2 = 0.4, RMSE = 0.28 mW m−2 sr−1 nm−1). These results demonstrate the need to account for the contribution of SIF emitted by the understory in the quantification of SIF within tree crowns and within the canopy from aggregated pixels in heterogeneous forest canopies

두 개의 기하학적 관찰 구성을 통합하는 자동화된 지상 기반 초 분광 시스템 개발

학위논문(석사) -- 서울대학교대학원 : 농업생명과학대학 협동과정 농림기상학, 2022. 8. 류영렬.Hyperspectral remote sensing is becoming a powerful tool for monitoring vegetation structure and functions. Especially, Sun-Induced chlorophyll fluorescence (SIF) and canopy reflectance monitoring have been widely used to understand physiological and structural changes in plants, and field spectroscopy has become established as an important technique for providing high spectral-, temporal resolution in-situ data as well as providing a means of scaling-up measurements from small areas to large areas. Recently, several tower-based remote sensing systems have been developed. However, in-situ studies have only monitored either BRF or BHR and there is still a lack of understanding of the geometric and optical differences in remote sensing observations, particularly between hemispheric-conical and bi-hemispheric configurations. Here, we developed an automated ground-based field spectroscopy system measuring far-red SIF and canopy hyperspectral reflectance (400–900 nm) with hemispherical-conical as well as bi-hemispherical configuration. To measure both bi-hemispherical and hemispherical-conical reflectance, we adopted a rotating prism by using a servo motor to face three types of ports that measure incoming-, outgoing irradiance and outgoing radiance. A white diffuse glass and collimating lens were used to measure the irradiance, and a collimating lens was used to measure the radiance with a field of view of 20 degrees. Additionally, we developed data management protocol that includes radiometric-, and wavelength calibrations. Finally, we report how BRF and BHR data differ in this system and investigated SIF and vegetation index from both hemispherical-conical and bi-hemispherical observation configurations for their ability to track GPP in the growing seasons of a deciduous broad-leaved forests.초 분광 원격 감지는 식생 구조와 기능을 모니터링하는 강력한 도구가 되고 있다. 특히, 식물의 생리적, 구조적 변화를 이해하기 위해 태양광 유도 엽록소 형광 (SIF)과 캐노피 반사율 모니터링이 널리 이용되고 있다. 현장 분광법은 높은 스펙트럼, 시간 분해능 현장 데이터를 제공하고 작은 영역에서 큰 영역으로 측정을 확장하는 수단을 제공하기 위한 중요한 기술로 확립되었다. 그러나, 수많은 연구가 현장 분광 시스템을 개발했지만, 반구-원추형 및 양 반구 구성 간의 원격 감지 관찰의 기하학적 및 광학적 차이에 대한 이해가 부족할 뿐만 아니라 초 분광 데이터를 지속적으로 수집하는 것은 여전히 어렵다. 우리는 반구형-원추형 및 이중 반구형 구성으로 원적외선 태양광 유도 엽록소 형광 및 캐노피 초 분광 반사율(400–900nm)을 측정하는 자동화된 지상 기반 필드 분광 시스템을 개발했다. 양방향 반사율과 반구형 원추형 반사율을 모두 측정하기 위해 서보 모터를 사용하여 프리즘을 회전하여 세가지 타입의 포트를 측정한다. 각 포트는 들어오는 복사 조도, 나가는 복사 조도 및 나가는 복사를 측정하는 세 가지 유형의 포트다. 조사조도는 백색확산유리와 굴절 렌즈를 사용하였고, 굴절 렌즈를 이용하여 조도를 측정하였다. 또한, 우리는 방사 측정 및 파장 교정을 포함하는 데이터 관리 프로토콜을 개발했다. 마지막으로, 우리는 낙엽 활엽수림의 성장기에 이 시스템에서 측정된 BRF와 BHR 데이터가 어떻게 다른지 보고하였다.Chapter 1. Introduction １ 1.1. Study Background １ 1.2. Purpose of Research ４ Chapter 2. Developing and Testing of Hyperspectral System ５ 2.1 Development of Hyperspectral System and Data Collecting ５ 2.1.1 The Central Control Unit and Spectrometer ５ 2.1.2 RotaPrism ７ 2.1.3 Data Collection ９ 2.3 Data Managing and Processing １１ 2.3.1 Preprocessing of Spectra １１ 2.3.2 Radiometric Calibration １３ 2.3.3 Retrieval of SIF and Vegetation Indices １５ 2.4 Ancillary Measurements to Monitoring Ecosystem. １７ Chapter 3. Application of Hyperspectral System １９ 3.1 Study Site １９ 3.2 Diurnal and Variation of Spectral Reflectance and SIF ２０ 3.3 Seasonal Variation of Vegetation Index and SIF ２２ 3.4 Broader Implications ２４ Chapter 4. Summary and Conclusions ２６ Bibliography ２８석