MSG Total and Diffuse Downward Surface Shortwave Flux (MDSSFTD, LSA-207)

NRT Product available since April 2020

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The MSG Total and Diffuse Downward Surface Shortwave Flux (MDSSFTD) product is an instantaneous estimate (every 15 minutes) of the total Downwelling Surface Short-wave radiative Flux (DSSF) (W/m2) and the fraction of the diffuse flux component to the total flux (unitless, between 0 - 1). The DSSF refers to the radiative energy in the wavelength interval [0.3 µm, 4.0 µm] reaching the Earth's surface per time and surface unit. An accurate knowledge of the spatio-temporal distribution of downwelling solar radiation and of its diffuse component at the surface are essential for understanding the climate processes at the Earth-atmosphere interface, but also for plant photosynthesis and carbon cycle.

 

Product Documentation

This pre-operational product is documented in the following documents:

Please see Product Peer-Review publications in References.

The use of LSA SAF products in publications is kindly requested to be duly acknowledged:
“The MDSSFTD product (Carrer et al., 2019a,b) was developed by CNRM/Météo-France thanks to the support of EUMETSAT. MDSSFTD data were provided by the EUMETSAT Satellite Application Facility on Land Surface Analysis (LSA SAF; Trigo et al., 2011)
http://lsa-saf.eumetsat.int


Trigo, I. F., C. C. DaCamara, P. Viterbo, J.-L. Roujean, F. Olesen, C. Barroso, F. Camacho-de Coca, D. Carrer, S. C. Freitas, J. García-Haro, B. Geiger, F. Gellens-Meulenberghs, N. Ghilain, J. Meliá, L. Pessanha, N. Siljamo, and A. Arboleda, 2011: The Satellite Application Facility on Land Surface Analysis. Int. J. Remote Sens., 32, 2725-2744, doi: 10.1080/01431161003743199

Carrer, D., Ceamanos, X., Moparthy, S., Vincent, C., C Freitas, S., & Trigo, I. F. (2019a). Satellite Retrieval of Downwelling Shortwave Surface Flux and Diffuse Fraction under All Sky Conditions in the Framework of the LSA SAF Program (Part 1: Methodology). Remote Sensing, 11(21), 2532.

 

Carrer, D., Moparthy, S., Vincent, C., Ceamanos, X., C Freitas, S., & Trigo, I. F. (2019b). Satellite Retrieval of Downwelling Shortwave Surface Flux and Diffuse Fraction under All Sky Conditions in the Framework of the LSA SAF Program (Part 2: Evaluation). Remote Sensing, 11(22), 2630.

MDSSFTD retrieval approach uses as input the three short-wave MSG/SEVIRI channels (VIS06, VIS08, NIR16), as well as information on cloud cover obtained from the Nowcasting and Very Short Range Forecasting Satellite Application Facility (NWC SAF). Dynamic information on the atmospheric water vapour content, ozone content, and aerosol optical depth are taken from the CAMS/ECMWF numerical weather prediction model. The MDAL surface albedo product (reference LSA-101) is also used as input to the processing, as well as the MSG top of atmosphere reflectances in the cloudy sky case only. The product output comprises the following datasets:

 

  • The total DSSF, named 'DSSF_TOT' in the MDSSFTD product;
  • The diffuse fraction of DSSF, named 'FRACTION_DIFFUSE';
  • The equivalent spectral AOD at 550nm for the current aerosol load, named 'AOD';
  • The opacity of the atmosphere, name 'OPACITY_INDEX';
  • The processing quality flags, named 'Q_FLAG'.

 

Algorithm Description

 

The method used for the retrieval of the MDSSFTD product is composed of two separated retrieval modules: one for clear sky conditions and one for the cloudy sky conditions. The presence of clouds in SEVIRI images is deduced for each pixel from the operational MSG NWC SAF cloud mask.

This algorithm is an upgrade of the LSA-SAF MDSSF (LSA-201) algorithm developed by Geiger et al. (2008). A detailed description of the method and of the performances are given in Carrer et al. (2019a,b). The upgrade includes a comprehensive representation of the influence of aerosols based on physical approximations of the radiative transfer within an atmosphere-surface associated medium.

 

Data Characteristics

The MDSSFTD product is computed within the area covered by the MSG full disk. For each time-slot, the DSSF estimate, the DSSF diffuse fraction, the equivalent spectral AOD at 550nm for the current aerosol composition, an index of the opacity of the atmosphere and the corresponding processing flag are disseminated in HDF5 format. The relevant information concerning the data fields is included in the HDF5 attributes.

 

Product Uncertainties

Carrer et al. 2019b shows that the satellite estimates of DSSF and the diffuse DSSF fraction (fd) meet the target requirements defined by the user community for all-sky (clear and cloudy) conditions. For DSSF, the requirements are 20 Wm-2 for DSSF < 200 Wm-2, and 10% for DSSF ≥ 200 Wm-2. The mean bias error (MBE) and relative mean bias error (rMBE) compared to the ground measurements are 3.618 Wm-2 and 0.252%, respectively. For fd, the requirements are 0.1 for fd < 0.5, and 20% for fd ≥ 0.5. The MBE and rMBE compared to the ground measurements are −0.044% and −17.699%, respectively.

In addition to inherent uncertainties due to methodological simplifications, the quality of the MDSSFTD product depends on the suitability of the cloud mask, the sensor performance (calibration uncertainty), and the accuracy of input information concerning the atmospheric constituents and the surface albedo. One of the major sources of uncertainty of the method used here is due to the estimate of the aerosol optical depth inputs (Ceamanos et al 2014).

Carrer, D., Ceamanos, X., Moparthy, S., Vincent, C., C Freitas, S., & Trigo, I. F. (2019a). Satellite Retrieval of Downwelling Shortwave Surface Flux and Diffuse Fraction under All Sky Conditions in the Framework of the LSA SAF Program (Part 1: Methodology). Remote Sensing, 11(21), 2532.

Carrer, D., Moparthy, S., Vincent, C., Ceamanos, X., C Freitas, S., & Trigo, I. F. (2019b). Satellite Retrieval of Downwelling Shortwave Surface Flux and Diffuse Fraction under All Sky Conditions in the Framework of the LSA SAF Program (Part 2: Evaluation). Remote Sensing, 11(22), 2630.
Carrer, D. et al. Land Surface Albedo and Down-Welling Short-Wave Radiation Retrievals using High Frequency Observations from MSG Geostationary Satellite. in Geoscience and Remote Sensing Symposium, 2008. IGARSS 2008. IEEE International 5, V–487 (IEEE, 2008).

Ceamanos, X., Carrer, D., Roujean, J.-L., 2014. Improved retrieval of direct and diffuse downwelling surface shortwave flux in cloudless atmosphere using dynamic estimates of aerosol content and type: application to the LSA-SAF project. Atmospheric Chem. Phys. 14, 8209–8232. doi:10.5194/acp-14-8209-2014

Geiger, B. et al. Near real-time provision of downwelling shortwave radiation estimates derived from satellite observations. Meteorological Applications 15, 411–420 (2008).

Ocean & Sea Ice SAF, 2002, Surface Solar Irradiance Product Manual, Version 1.2

Reindl DT, Beckman WA, Duffie JA. Diffuse fraction correlations. Solar Energy 1990;45:1–7.