Fig.1 Instantaneous distribution of irradiance at the surface of the Baltic Sea Fig.2 Areas where total solar radiation was measured from the r/v “Oceania” in 2010-2012

Short-wave solar radiation

The short-wave solar radiation at the sea surface. The flux density (downward vector irradiance[1]) of solar radiation (wavelength range 300-4000 nm) incident on the sea surface and scattered in the atmosphere. Apart from instantaneous values measured every 15 minutes and expressed in [Wm^-2] with a spatial resolution of 1 km, the SatBałtyk system also provides maps of daily sums of this flux (as a component of the radiation budget).

Methodology The SolRad model is used to determine the magnitude of the downward short-wave radiation flux. The values obtained every 15 minutes are then used to calculate daily totals (doses) of irradiance energy. The input data for the model are obtained from the SEVIRI radiometer (HRV spectral channel) deployed on MSG series satellites, AVHRR, TOVS and SBUV/2 radiometers deployed on satellites of the TirosN/NOAA and Metop series, and from the UM or WRF meteorological models. Validation 

The statistical error is expressed as the standard deviation between the fluxes measured in situ and those calculated using the SolRad model:

$$\sigma_{\epsilon}=\sqrt{\frac{1}{N}(\Sigma(X_{i,C}-X_{i,M})^2)}$$

where N – number of cases, X_i,C – measured value, X_i,M – calculated value (modelled). The systematic error (the mean difference between the measured and calculated values):

$$<\epsilon>=N^{-1}\sum_{i}\epsilon_{i}$$

$$\epsilon_{i}=(X_{i,C}-X_{i,M})/X_{i,M}$$

is defined with respect to measurements made from on board r/v “Oceania” at the stations shown on Fig. 2 in 2010-2012. The errors calculated for various angles of incidence of solar radiation are given in Table 1.

Table 1. The results of validation of instantaneous irradiance values determined by the SolRad model with respect to in situ measurements (all values in [Wm^-2]; variable : E_d(Oceania)-E_d(SolRad)

[1] Dera J., 2003, Fizyka Morza, PWN, Warszawa, 541

[2] SolRad - model Solar Radiation