The brine and gas content of sea ice with attention to low salinities and high temperatures

Based on the well known sea ice phase diagram, equations are derived for determining the brine and gas content of sea Ice for high temperatures (range 0 to -2 °C) and low salinities. The presently widely used equations of Cox and Weeks (1982) are valid only for temperatures below -2°C. Fresh-water ice is used as a boundary condition for the equations. The relative salt concentrations in brine are_assumed to be the same as in normal (or standard) seawater. Two sets of equations are presented: 1) accurate formulae based on UNESCO standard sea water equations, and 2) approximate formulae based on general properties of weak solutions. The approximate formulae are not essentially different from the classical system which basically assumes the freezing point to be a linear function of fractional salt content. The agreement between the two approaches is excellent and the approximate system is good enough for most applications

Influence of forest floor vegetation on the total forest reflectance and its implications for LAI estimation using vegetation indices

Recently a simple analytic canopy bidirectional reflectance factor (BRF) model based on the spectral invariants theory was presented. The model takes into account that the recollision probability in the forest canopy is different for the first scattering than the later ones. Here this model is extended to include the forest floor contribution to the total forest BRF. The effect of the understory vegetation on the total forest BRF as well as on the simple ratio (SR) and the normalized difference (NDVI) vegetation indices is demonstrated for typical cases of boreal forest. The relative contribution of the forest floor to the total BRF was up to 69 % in the red wavelength range and up to 54 % in the NIR wavelength range. Values of SR and NDVI for the forest and the canopy differed within 10 % and 30 % in red and within 1 % and 10 % in the NIR wavelength range. The relative variation of the BRF with the azimuth and view zenith angles was not very sensitive to the forest floor vegetation. Hence, linear correlation of the modelled total BRF and the Ross-thick kernel was strong for dense forests (R2 > 0.9). The agreement between modelled BRF and satellite-based reflectance values was good when measured LAI, clumping index and leaf single scattering albedo values for a boreal forest were used as input to the model.Hiljattain on esitetty yksinkertainen analyyttinen puuston kaksisuuntaisen heijastuskertoimen (BRF) malli, joka perustuu spketristä riippumattomien parametrien teoriaan. Mallissa otetaan huomioon, että fotonin uudelleen siroamisen todennäköisyys metsässä poikkeaa ensimmäisellä kerralla sen myöhemmistä arvoista. Tässä tutkimuksessa mallia on edelleen kehitetty siten, että siinä huomioidaan metsän pohjan osuus metsän BRF:stä. Aluskasvillisuuden vaikutusta BRF:ään ja kasvillisuusindekseihin SR (yksinkertainen suhde) ja NDVI (normalisoitu kasvillisuuden erotusindeksi) havainnollistetaan esimerkeillä tyypillisestä boreaalisesta metsästä. Metsän pohjan suhteellinen osuus BRF:stä ulottui 69 prosenttiin punaisen alueen aallonpituuksilla ja 54 prosenttiin lähiinfrapunan aallonpituusalueella. Metsälle laskettujen SR:n ja NDVI:n arvot poikkesivat pelkälle puustolle lasketuista vastaavista arvoista 10 % ja 30 % punaisella aallonpituusalueella ja 1 % ja 10 % lähi-infrapunan aallonpituusalueella. BRF:n suhteellinen muutos katselukulmien vaihdellessa ei ollut kovin herkkä metsän pohjakasvillisuudelle. Siten mallinnettu metsän BRF oli lineaarisesti verrannollinen Ross:n tiheän metsän kerneliin (selitysaste > 0.9). Mallinnettu BRF ja satellidatasta peräisin olevat reflektanssiarvot vastasivat hyvin toisiaan, kun mallin syöttötietoina käytettiin boreaalisen metsän mitattuja lehtialaindeksin, ryhmittyneisyysindeksin ja lehden albedon arvoja

Method for constructing an AOD-related atmospheric correction time series for the CLARA-A2 SAL data record

In the Satellite Application Facility on Climate Monitoring (CM SAF) project, financially supported by EUMETSAT, the 34-year long (1982-2015) broadband albedo time series CLARA-A2 SAL (the Surface ALbedo from the CM SAF cLoud, Albedo and RAdiation data record, second version) was produced from Advanced Very High Resolution Radiometer (AVHRR) measurements. CLARA-A2 SAL data record uses a Simplified Method for Atmospheric Correction algorithm SMAC for correcting for atmospheric effects. Aerosol optical depth (AOD) is the main input of the algorithm. Because there were no global AOD time series for the whole needed time period (1982-2015), the AOD-related time series were constructed, and the method for calculating it is described in this report

A Simple Method to Determine the Timing of Snow Melt by Remote Sensing with Application to the CO2 Balances of Northern Mire and Heath Ecosystems

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Estimating forest leaf area index using satellite images : comparison of k-NN based Landsat-NFI LAI with MODIS-RSR based LAI product for Finland

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Validation of MODIS and GEOV1 fPAR Products in a Boreal Forest Site in Finland

Creative Commons Attribution License (CC BY 4.0)Remote sensing of the fraction of absorbed Photosynthetically Active Radiation (fPAR) has become a timely option to monitor forest productivity. However, only a few studies have had ground reference fPAR datasets containing both forest canopy and understory fPAR from boreal forests for the validation of satellite products. The aim of this paper was to assess the performance of two currently available satellite-based fPAR products: MODIS fPAR (MOD15A2, C5) and GEOV1 fPAR (g2_BIOPAR_FAPAR), as well as an NDVI-fPAR relationship applied to the MODIS surface reflectance product and a Landsat 8 image, in a boreal forest site in Finland. Our study area covered 16 km(2) and field data were collected from 307 forest plots. For all plots, we obtained both forest canopy fPAR and understory fPAR. The ground reference total fPAR agreed better with GEOV1 fPAR than with MODIS fPAR, which showed much more temporal variation during the peak-season than GEOV1 fPAR. At the chosen intercomparison date in peak growing season, MODIS NDVI based fPAR estimates were similar to GEOV1 fPAR, and produced on average 0.01 fPAR units smaller fPAR estimates than ground reference total fPAR. MODIS fPAR and Landsat 8 NDVI based fPAR estimates were similar to forest canopy fPAR.Peer reviewe

Geographical gradients in boreal forest albedo and structure in Finland

Correction: DOI:10.1016/j.rse.2014.08.018Land surface albedo is an essential climate variable controlling the planetary radiative energy budget, yet it is still among the main uncertainties of the radiation budget in the current climate modeling. To date, albedo satellite products have not been linked to extensive forest inventory data sets due to the lack of ground reference data. Here, we used comprehensive and detailed maps of forest inventory variables to couple forest structure and MODIS albedo products for both winter and summer conditions. We investigated how the relationships between forest variables and albedo change seasonally and along latitudinal gradients in the forest biomes of Finland between 60° and 70° N. We observed an increase in forest albedo with increasing latitude in winter but not in summer. Also, relationships between forest variables and the black-sky albedo or directional–hemispherical reflectance (DHR) at different latitudes were tighter in winter than in summer, especially for forest biomass. Summer albedo was only weakly correlated with the traditional inventory variables. Our findings suggest that the relationships between forest variables and DHR depend on latitude.Peer reviewe