Synergy of earth observation data to advance monitoring of optically complex waters
Date
2024-05-13
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Abstract
Järved ja rannikualad on veeökosüsteemi väga olulised osad, mistõttu on järjepidev seire vajalik. Neid mõjutavad inimtekkelised tegurid, kuid arvesse tuleks ka võtta looduslikke tegureid, nagu päevast ja sesoonset dünaamikat. Kopernikuse programmi satelliitidel Sentinel-2 ja Sentinel-3 on potentsiaal täiendada veekvaliteedi seiret Euroopa Liidu Veepoliitika Raamdirektiivi alusel. Satelliidiandmete kasutamine veekogude seireks on aga keeruline atmosfääri koostise, vees sisalduvate optiliselt aktiivsete ainete ja kalda mõju tõttu. Nendel põhinevate rakenduste arendamiseks on oluline kogu kaugseire andmete töötlemisahel. Oluline on vähendada mõõtemääramatusi igas töötlemisahelas alustades satelliidiandmete valideerimiseest kohapeal mõõdetud andmetega kuni rakenduse lõpliku väljatöötamiseni. Käesolev töö näitas, et tuleb lähtuda uuritavast parameetrist, veetüübist ja maapinna mõjust. Kuna klorofüll a on põhiparameeter vee ökoloogilise seisundi hindamisel, siis töös testiti ja arendati klorofüll a algoritme Sentinel-2 satelliidi jaoks, millel on sobiv ruumiline lahutus väikeste järvede seireks. Nii kohapeal mõõdetud andmete kui ka satelliidiandmete kombineerimine võib parandada ökoloogilise seisundi hindamist, sest rohkem andmeid on kättesaadavamad, mis võimaldab näha dünaamikat ja suundumusi. Töös leiti, et klorofüll a algoritmide sobivus sõltus optilisest veetüübist ja seetõttu leiti sobivad algoritmid. Ökoloogilise seisundi hindamise parandamiseks loodi optiliste ja altimeetria andmete vahel sünergia, et eemaldada veetaseme mõju veekvaliteedi parameetritest. Selline lähenemisviis arendab seirevõimalusi kasutades kaugseire andmeid hinnates veekogude ökoloogilist seisundit.
Lakes and coastal areas are very important parts of the aquatic ecosystem, therefore consistent monitoring is essential. They are influenced by antrophogenic factors, but also natural factors should be taken into account, such as daily and seasonal dynamics. Copernicus programme satellites Sentinel-2 and Sentinel-3 have great potential to complement current water quality monitoring under European Union Water Framework Directive. However, using satellite data for monitoring waterbodies is challenging because of atmospheric composition, different amount of optically active substances in water and influence from the vicinity of the land. For developing satellite-based applications, the whole Earth Observation processing chain is crucial. Minimizing uncertainties in each processing chain is essential, starting from the reference data for validating the satellite data until the final application development. The study found that satellite data processing has to consider the parameter of interest, optical water type and the vicinity of land of the target waterbody. As Chlorophyll a is the key parameter for estimating the ecological status of water, Chlorophyll a algorithms were tested and developed for Sentinel-2 satellite, which has suitable resolution for monitoring small lakes. The inclusion of both in situ and satellite data could improve the ecological status assessment in terms of data availability showing more dynamics and trends. It was found that the suitability of Chlorophyll a algorithms was dependent on optical water types and most suitable algorithms were found. To improve the assessment of ecological status, the synergy between optical and altimetry data was created to remove water level influence from water quality parameters. This approach will advance monitoring in terms of assessment of ecological status under the Water Framework Directive derived by Earth Observation data.
Lakes and coastal areas are very important parts of the aquatic ecosystem, therefore consistent monitoring is essential. They are influenced by antrophogenic factors, but also natural factors should be taken into account, such as daily and seasonal dynamics. Copernicus programme satellites Sentinel-2 and Sentinel-3 have great potential to complement current water quality monitoring under European Union Water Framework Directive. However, using satellite data for monitoring waterbodies is challenging because of atmospheric composition, different amount of optically active substances in water and influence from the vicinity of the land. For developing satellite-based applications, the whole Earth Observation processing chain is crucial. Minimizing uncertainties in each processing chain is essential, starting from the reference data for validating the satellite data until the final application development. The study found that satellite data processing has to consider the parameter of interest, optical water type and the vicinity of land of the target waterbody. As Chlorophyll a is the key parameter for estimating the ecological status of water, Chlorophyll a algorithms were tested and developed for Sentinel-2 satellite, which has suitable resolution for monitoring small lakes. The inclusion of both in situ and satellite data could improve the ecological status assessment in terms of data availability showing more dynamics and trends. It was found that the suitability of Chlorophyll a algorithms was dependent on optical water types and most suitable algorithms were found. To improve the assessment of ecological status, the synergy between optical and altimetry data was created to remove water level influence from water quality parameters. This approach will advance monitoring in terms of assessment of ecological status under the Water Framework Directive derived by Earth Observation data.
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