Search

2007. aastal rajati Järvseljal kolm ühe hektari suurust katseala, kui kaardistati ja mõõdeti üle kõik puud simulatsioon eksperimentide korraldamiseks (Kuusk, et al., 2013; Widlowski et al., 2015). Need kolm puistut (vt fotod lisas 1) esindavad tüüpilist liitunud võrastikuga kuusikut, kaasikut ja siirdesoo männikut. Kaasikus oli tehtud 2004. aastal harvendusraie, 2018. aastal puhastati katseala alusmetsast, et valmistada ala ette maapealse laser skanneriga mõõtmisteks. Kuusikus ja männikus teadaolevalt viimase 30 aasta jooksul raieid tehtud ei ole. Katsealade (joonised 1, 3, 5) nurkade koordinaadid on mõõdetud diferentsiaal-GPS meetodiga peale mahamärkimist (tabel 1). 2019. aasta kordus mõõtmiste tulemusena ilmnes, et puistute rinnaspindala, keskmine kõrgus ning keskmise puu rinnasläbimõõt olid kasvanud (tabelid 2–4). Puude arv oli kahanenud kõigis puistutes, välja arvatud kaasikus, kus 2018. aasta puhastus raie käigus jäeti alles selleks ajaks 4 cm rinnasdiameetri saavutanud puud. Kuusikus saadi tulemuseks, et võrade raadiused olid võrreldes 2007. aastaga kahanenud. Kas tegemist on võra projektsiooni välispiiri erineva tõlgendamise või tegelikult toimunud muutusega, võiks edaspidi selguda 2013. (Kuusk et al., 2015) ja 2019. aastal tehtud maapealse laserskanneri mõõtmiste andmete analüüsist.

Terrestrial laser scanner (TLS) measurements were carried out in mature birch, pine, and spruce stands in Järvselja, Estonia. The structure of stands has been previously studied. A simple special clustering procedure is developed for automatic detection of stem positions and estimation of tree stem dimensions from the TLS point cloud. Tree stem diameter at breast height (DBH), vertical profile of stem and size distribution of DBH is estimated with high precision in the pine stand where the second growth tree layer is almost missing. The presence of second growth limits estimating stem dimensions accurately in the birch stand, and the procedure fails in the dense spruce stand of rich undergrowth and low dead branches. In such stands the TLS measurements should be done in dense grid with short-range sounding setup only. The developed procedure is undemanding for computers and can be applied on simple PC-s.

Systematic spectral measurements of downwelling solar radiation, both of global and diffuse, have been collected in summertime during 8 years in the hemi-boreal zone in south east Estonia near the SMEAR-Estonia research station. The measurements provided information about the variation of spectral and total fluxes of downwelling hemispherical global and diffuse solar radiation in the wavelength range from 300 to 2160 nm with spectral resolution of 3 nm in UV to 16 nm in SWIR spectral regions. Unique data have been collected and quantitative description of the variability of the measured spectra is provided. For the description of the synoptic situation during measurements, instead of cloud cover, the ratio of measured to possible total flux in the spectral range of 320–1800 nm is used. This ratio could be used as the primary meteorological parameter instead of cloud cover which is difficult to measure instrumentally. [ABSTRACT FROM AUTHOR]

Forest reflectance models are able to contribute to the interpretation of satellite images over forested areas. A multipurpose forest reflectance model is briefly described.

The information about variable components of the atmosphere (aerosol, water vapour, and ozone) during acquisition is required for the atmospheric correction of spectral images acquired by shortwave sensors of the Earth observing remote-sensing satellites. The procedure to estimate aerosol optical depth and columnar water vapour by the inversion of the atmospheric radiative transfer model 6S using moderate-resolution spectra of incident solar radiation is proposed. Comparison to the results obtained by the Aerosol Robotic Network AERONET at an AERONET site at the distance of 50 km on days when both sensors were in the same air mass shows systematic overestimation both of aerosol optical depth and of columnar water vapour if aerosol optical depth is estimated in the wavelength range of 365-425 nm and columnar water in the range of 895-985 nm using spectra of total irradiance. If more wavelengths and diffuse-to-total spectral irradiance ratio are implemented in the inversion, the bias of estimated water vapour decreases, but aerosol optical depth is underestimated. The estimates at 50 km distance are well correlated. The modelled spectral irradiance using estimated atmospheric parameters matches the measured spectra with high accuracy. In the spectral bands of the Sentinel-2 MultiSpectral Instrument (MSI), the differences do not exceed 2%. [ABSTRACT FROM AUTHOR]