Dark Signal Temperature Dependence Correction Method for Miniature Spectrometer Modules

A dark signal temperature dependence correction method for miniature spectrometer modules is described in this paper. It is based on laboratory measurements of dark signal temperature dependence at few different integration times. A set of parameters are calculated which make it possible to estimate dark signal at any temperature and integration time within reasonable range. In field conditions, it is not always possible to take frequent dark signal readings during spectral measurements. If temperature is recorded during the measurement, this method can be used for estimating dark signal for every single spectral measurement. The method is validated on two different miniature spectrometers

STY1 and STY2 promote the formation of apical tissues during Arabidopsis gynoecium development

Gynoecium ontogenesis in Arabidopsis is accomplished by the co-ordinated activity of genes that control patterning and the regional differentiation of tissues, and ultimately results in the formation of a basal ovary, a short style and an apical stigma. A transposon insertion in the STYLISH1 (STY1) gene results in gynoecia with aberrant style morphology, while an insertion mutation in the closely related STYLISH2 (STY2) gene has no visible effect on gynoecium development. However, sty1-1 sty2-1 double mutant plants exhibit an enhanced sty1-1 mutant phenotype and are characterized by a further reduction in the amount of stylar and stigmatic tissues and decreased proliferation of stylar xylem. These data imply that STY1 and STY2 are partially redundant and that both genes promote style and stigma formation and influence vascular development during Arabidopsis gynoecium development. Consistently, STY1 and STY2 are expressed in the apical parts of the developing gynoecium and ectopic expression of either STY1 or STY2 driven by the CaMV 35S promoter is sufficient to transform valve cells into style cells. STY1::GUS and STY2::GUS activity is detected in many other organs as well as the gynoecium, suggesting that STY1 and STY2 may have additional functions. This is supported by the sty1-1 sty2-1 double mutants producing rosette and cauline leaves with a higher degree of serration than wild-type leaves. STY1 and STY2 are members of a small gene family, and encode proteins with a RING finger-like motif. Double mutant analyses indicate that STY1 genetically interacts with SPATULA and possibly also with CRABS CLAW

A Review of Protocols for Fiducial Reference Measurements of Water-Leaving Radiance for Validation of Satellite Remote-Sensing Data over Water

This paper reviews the state of the art of protocols for measurement of water-leaving radiance in the context of fiducial reference measurements (FRM) of water reflectance for satellite validation. Measurement of water reflectance requires the measurement of water-leaving radiance and downwelling irradiance just above water. For the former there are four generic families of method, based on: (1) underwater radiometry at fixed depths; or (2) underwater radiometry with vertical profiling; or (3) above-water radiometry with skyglint correction; or (4) on-water radiometry with skylight blocked. Each method is described generically in the FRM context with reference to the measurement equation, documented implementations and the intra-method diversity of deployment platform and practice. Ideal measurement conditions are stated, practical recommendations are provided on best practice and guidelines for estimating the measurement uncertainty are provided for each protocol-related component of the measurement uncertainty budget. The state of the art for measurement of water-leaving radiance is summarized, future perspectives are outlined, and the question of which method is best adapted to various circumstances (water type, wavelength) is discussed. This review is based on practice and papers of the aquatic optics community for the validation of water reflectance estimated from satellite data but can be relevant also for other applications such as the development or validation of algorithms for remote-sensing estimation of water constituents including chlorophyll a concentration, inherent optical properties and related products

A review of protocols for fiducial reference measurements of water-leaving radiance for validation of satellite remote-sensing data over water

© 2019 by the authors. This paper reviews the state of the art of protocols for measurement of water-leaving radiance in the context of fiducial reference measurements (FRM) of water reflectance for satellite validation. Measurement of water reflectance requires the measurement of water-leaving radiance and downwelling irradiance just above water. For the former there are four generic families of method, based on: (1) underwater radiometry at fixed depths; or (2) underwater radiometry with vertical profiling; or (3) above-water radiometry with skyglint correction; or (4) on-water radiometry with skylight blocked. Each method is described generically in the FRM context with reference to the measurement equation, documented implementations and the intra-method diversity of deployment platform and practice. Ideal measurement conditions are stated, practical recommendations are provided on best practice and guidelines for estimating the measurement uncertainty are provided for each protocol-related component of the measurement uncertainty budget. The state of the art for measurement of water-leaving radiance is summarized, future perspectives are outlined, and the question of which method is best adapted to various circumstances (water type, wavelength) is discussed. This review is based on practice and papers of the aquatic optics community for the validation of water reflectance estimated from satellite data but can be relevant also for other applications such as the development or validation of algorithms for remote-sensing estimation of water constituents including chlorophyll a concentration, inherent optical properties and related products

Sun-Induced Chlorophyll Fluorescence I: Instrumental Considerations for Proximal Spectroradiometers

Growing interest in the proximal sensing of sun‐induced chlorophyll fluorescence (SIF) has been boosted by space-based retrievals and up-coming missions such as the FLuorescence EXplorer (FLEX). The European COST Action ES1309 “Innovative optical tools for proximal sensing of ecophysiological processes” (OPTIMISE, ES1309; https://optimise.dcs.aber.ac.uk/) has produced three manuscripts addressing the main current challenges in this field. This article provides a framework to model the impact of different instrument noise and bias on the retrieval of SIF; and to assess uncertainty requirements for the calibration and characterization of state-of-the-art SIF-oriented spectroradiometers. We developed a sensor simulator capable of reproducing biases and noises usually found in field spectroradiometers. First the sensor simulator was calibrated and characterized using synthetic datasets of known uncertainties defined from laboratory measurements and literature. Secondly, we used the sensor simulator and the characterized sensor models to simulate the acquisition of atmospheric and vegetation radiances from a synthetic dataset. Each of the sensor models predicted biases with propagated uncertainties that modified the simulated measurements as a function of different factors. Finally, the impact of each sensor model on SIF retrieval was analyzed. Results show that SIF retrieval can be significantly affected in situations where reflectance factors are barely modified. SIF errors were found to correlate with drivers of instrumental-induced biases which are as also drivers of plant physiology. This jeopardizes not only the retrieval of SIF, but also the understanding of its relationship with vegetation function, the study of diel and seasonal cycles and the validation of remote sensing SIF products. Further work is needed to determine the optimal requirements in terms of sensor design, characterization and signal correction for SIF retrieval by proximal sensing. In addition, evaluation/validation methods to characterize and correct instrumental responses should be developed and used to test sensors performance in operational conditions

A review of protocols for Fiducial Reference Measurements of downwelling irradiance for the validation of satellite remote sensing data over water

This paper reviews the state of the art of protocols for the measurement of downwelling irradiance in the context of Fiducial Reference Measurements (FRM) of water reflectance for satellite validation. The measurement of water reflectance requires the measurement of water-leaving radiance and downwelling irradiance just above water. For the latter, there are four generic families of method, using: (1) an above-water upward-pointing irradiance sensor; (2) an above-water downward-pointing radiance sensor and a reflective plaque; (3) a Sun-pointing radiance sensor (sunphotometer); or (4) an underwater upward-pointing irradiance sensor deployed at different depths. Each method-except for the fourth, which is considered obsolete for the measurement of above-water downwelling irradiance-is described generically in the FRM context with reference to the measurement equation, documented implementations, and the intra-method diversity of deployment platform and practice. Ideal measurement conditions are stated, practical recommendations are provided on best practice, and guidelines for estimating the measurement uncertainty are provided for each protocol-related component of the measurement uncertainty budget. The state of the art for the measurement of downwelling irradiance is summarized, future perspectives are outlined, and key debates such as the use of reflectance plaques with calibrated or uncalibrated radiometers are presented. This review is based on the practice and studies of the aquatic optics community and the validation of water reflectance, but is also relevant to land radiation monitoring and the validation of satellite-derived land surface reflectance

The fourth phase of the radiative transfer model intercomparison (RAMI) exercise : Actual canopy scenarios and conformity testing

The RAdiative transfer Model Intercomparison (RAMI) activity focuses on the benchmarking of canopy radiative transfer (RT) models. For the current fourth phase of RAMI, six highly realistic virtual plant environments were constructed on the basis of intensive field data collected from (both deciduous and coniferous) forest stands as well as test sites in Europe and South Africa. Twelve RT modelling groups provided simulations of canopy scale (directional and hemispherically integrated) radiative quantities, as well as a series of binary hemispherical photographs acquired from different locations within the virtual canopies. The simulation results showed much greater variance than those recently analysed for the abstract canopy scenarios of RAMI-IV. Canopy complexity is among the most likely drivers behind operator induced errors that gave rise to the discrepancies. Conformity testing was introduced to separate the simulation results into acceptable and non-acceptable contributions. More specifically, a shared risk approach is used to evaluate the compliance of RI model simulations on the basis of reference data generated with the weighted ensemble averaging technique from ISO-13528. However, using concepts from legal metrology, the uncertainty of this reference solution will be shown to prevent a confident assessment of model performance with respect to the selected tolerance intervals. As an alternative, guarded risk decision rules will be presented to account explicitly for the uncertainty associated with the reference and candidate methods. Both guarded acceptance and guarded rejection approaches are used to make confident statements about the acceptance and/or rejection of RT model simulations with respect to the predefined tolerance intervals. (C) 2015 The Authors. Published by Elsevier Inc.Peer reviewe

WATERHYPERNET: a prototype network of automated in situ measurements of hyperspectral water reflectance for satellite validation and water quality monitoring

This paper describes a prototype network of automated in situ measurements of hyperspectral water reflectance suitable for satellite validation and water quality monitoring. Radiometric validation of satellite-derived water reflectance is essential to ensure that only reliable data, e.g., for estimating water quality parameters such as chlorophyll a concentration, reach end-users. Analysis of the differences between satellite and in situ water reflectance measurements, particularly unmasked outliers, can provide recommendations on where satellite data processing algorithms need to be improved. In a massively multi-mission context, including Newspace constellations, hyperspectral missions and missions with broad spectral bands not designed for “water colour”, the advantage of hyperspectral over multispectral in situ measurements is clear. Two hyperspectral measurement systems, PANTHYR (based on the mature TRIOS/RAMSES radiometer) and HYPSTAR® (a newly designed radiometer), have been integrated here in the WATERHYPERNET network with SI-traceable calibration and characterisation. The systems have common data acquisition protocol, data processing and quality control. The choice of validation site and viewing geometry and installation considerations are described in detail. Three demonstration cases are described: 1. PANTHYR data from two sites are used to validate Sentinel-2/MSI (A&B); 2. HYPSTAR® data at six sites are used to validate Sentinel-3/OLCI (A&B); 3. PANTHYR and HYPSTAR® data in Belgian North Sea waters are used to monitor phytoplankton parameters, including Phaeocystis globosa, over two 5 month periods. Conclusion are drawn regarding the quality of Sentinel-2/MSI and Sentinel-3/OLCI data, including indications where improvements could be made. For example, a positive bias (mean difference) is found for ACOLITE_DSF processing of Sentinel-2 in clear waters (Acqua Alta) and clues are provided on how to improve this processing. The utility of these in situ measurements, even without accompanying hyperspectral satellite data, is demonstrated for phytoplankton monitoring. The future evolution of the WATERHYPERNET network is outlined, including geographical expansion, improvements to hardware reliability and to the measurement method (including uncertainty estimation) and plans for daily distribution of near real-time data

Metsade atmosfäärialuse spektraalse peegelduskoefitsiendi mõõtmine taimkatte kiirguslevimudelite arendamiseks

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Taimestik mõjutab kogu ökosüsteemi ja kliimat. Selle uurimine ja jälgimine on seetõtu olnud läbi aegade kaugseire üks olulisemaid valdkondi. Kaugseiresatelliitide levik 20. sajandi teisest poolest alates on oluliselt laiendanud kaugseire võimalusi. Et mõõdetud andmetest mingit sisulist infot eraldada, on vaja aru saada, kuidas mõõdetav signaal moodustub ja mis seda mõjutab. Taimkatte kiirguslevimudelid hõlmavadki endas seda teadmiste baasi. Nad võimaldavad arvutada, kuidas metsale langev päikesekiirgus neeldub ja hajub olenevalt taimkatte struktuurist ja optilistest omadustest. Mudelite arendamiseks on vaja mõõtmistulemusi reaalsest elust, et neid saaks võrrelda modelleeritud andmetega ning erinevuse korral mudelit parandada. Samuti saab atmosfäärialuste mõõtmiste abil kontrollida ja vajadusel parandada satelliidipildi atmosfäärikorrektsiooni ja satelliidisensori kalibratsioonikoefitsiente. Käesoleva töö eesmärgiks oli välja töötada ning valmistada sobilik aparatuur metsade atmosfäärialuse spektraalse peegelduskoefitsiendi mõõtmiseks ja reaalsete mõõtmiste läbiviimine. Töö käigus on valminud spektromeetrite seeria UAVSpec. Alates 2006. aastast on igal suvel Eesti Maaülikooli Järvselja Katse- ja Õppemetskonnas mõõdetud mehitatud helikopterilt metsade spektraalset heledust. Algusest peale on silmas peetud võimalust kasutada UAVSpec spektromeetrite kandurina mehitamata lennuvahendit, mistõttu on spektromeetrid disainitud täisautonoomsed ning piisavalt väiksed ja kerged. Spektromeetrite olulisemad omadused parametriseeriti laborimõõtmiste põhjal ning koostati algoritmid registreeritud signaalide radiomeetriliseks korrektsiooniks. Taimkatte kiirguslevimudelid vajavad väga suurt hulka sisendparameetreid, mida tavapärase metsa takseerimise käigus ei mõõdeta. Seetõttu koostati mahukas andmekogum kolme 1-hektarilise puistu kohta. Tartu Observatooriumis väljatöötatud metsa peegeldusmudeliga FRT simuleeriti nende puistute peegeldusspektreid ning võrreldi neid mõõtmistulemustega. Pakuti välja põhjalik protsessikirjeldus atmosfäärialuste tugimõõtmiste toel satelliidipiltide töötlemiseks ja satelliitsensorite kalibratsiooniks.Vegetation influences the whole ecosystem and climate. Its research and monitoring has therefore always been one of the most important fields of remote sensing. The spread of Earth observation satellites at the second half of the 20th century has dramatically expanded the possibilities for remote sensing. To extract some useful information from the measured data, it is necessary to understand how the measured signal is formed and what affects it. Radiative transfer models represent our perception of photon transport in vegetation canopies. They can simulate how the incident solar radiation is absorbed and scattered by forests, depending on the vegetation structure and optical properties. Ground truth data is needed for developing the models. By comparing the measured and modelled data, it is possible to validate and improve the model. Top-of-canopy reflectance measurements can also be used for validating the atmospheric correction of satellite images and for vicarious calibration of satellite sensors. The aim of this study was designing an autonomous spectrometer system suitable for measuring the top-of-canopy reflectance of forests from a lightweight carrier, such as an unmanned aerial vehicle (UAV). In the course of this study the UAVSpec-series spectrometer systems have been designed and built. Since 2006 the top-of-canopy spectral directional reflectance of forest stands has been measured every summer in the Järvselja Training and Experimental Forestry District of the Estonian University of Life Sciences. Dark signal temperature dependence and instrument function of the spectrometers were determined in the laboratory. In order to guarantee the metrological quality of spectroscopic measurements, these parameters are taken into account in the data processing workflow. Vegetation radiative transfer models need many input parameters which are not measured during ordinary forest inventories. Therefore, an exhaustive dataset was compiled for three 1-hectare stands in Järvselja. The forest reflectance model FRT developed at the Tartu Observatory was used for modelling the reflectance of these stands and the results were compared with the measured data. A detailed workflow description was proposed for processing satellite imagery and calibrating satellite sensors