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Satellite Cloud Mask


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Satellite Cloud Mask

  1. 1. Satellite monitoring of solar radiation I Parallax Correction II Cloud-Mask e Shadow-Mask III Daily insolation map IV Total water content (TWC) retrieve using multispectral techniques Matteo Masotti Freitag 24 juli 2009
  2. 2. Parallax correction in Ir10.8  m channel <ul><li>The so-called parallax effect is a considerable geometrical effect associated with satellite measurements. It is more important even when we are observing high clouds, far from the nadir. This means that the location of clouds above European territory moves away from their real position. </li></ul><ul><li>It depends on: </li></ul><ul><li>Cloud top height (that's why we use 10.8  m Brightness Temperature information) </li></ul><ul><li>Cloud coordinates </li></ul><ul><li>Satellite viewing angle </li></ul>IR brightness temperature from Sat and temperature profile given by numerical model are combined to extract information about cloud height and consequently the extent of parallax correction. Freitag 24 juli 2009
  3. 3. Parallax <ul><li>20090408 hh 2330 Corrected 10.8  m Image </li></ul>20090408 hh 2330 Original 10.8  m Image Colder clouds top height displacements are in the south-west direction in comparison to original image Zoom Corr Zoom Orig Temp °C Freitag 24 juli 2009
  4. 4. Cloud Mask Vis 0.8  m and Ir 10.8  m Combination of informations provided by Vis 0.8  m (reflectance) and Ir 10.8  m (Brightness temperature) channels. Comparison with clear sky threshold values from the previous 7 days. Milano Cloud Mask 16/04/2009 06:45 UTC I n p u t Freitag 24 juli 2009
  5. 5. Cloud Mask threshold Visible Infrared Freitag 24 juli 2009 Minimum of reflectance during 7 days and associated variance Maximum of Bright. Temp. During 7 days and associated variance For each pixel
  6. 6. Cloud Mask Vis 0.8  m e Ir 10.8  m Cloud index (YES/NO) of every geolocated pixel and quality flag associated Milano Cloud Mask 16/04/2009 06:45 UTC It is important for beam radiation information associated to PV plants and cocentrating solar systems. Daily insolation map New solar plants planification O u t p u t Freitag 24 juli 2009
  7. 7. Shadowing Shadowing effect has to be taken into account in the estimate of daily insolation Reflectance is strongly influenced by cloud shadow, specifically it is related to signal reduction and then to a lack of information over the associated pixel In order to assign cloud cover classification over pixels, information about sun position (Solar zenith and azimuth angle) and cloud position need to be calculated. Freitag 24 juli 2009 Shadowing effect is strongly related to solar zenith angle. The increase of solar zenith angle (sunrise and sunset) affects growing areas of the domain.
  8. 8. Daily insolation map Freitag 24 juli 2009 Normalized clear sky day-light duration 0 completely Cloudy 1 completely Clear sky Spatial resolution 3.5 Km Combination of informations from cloud mask (parallax corrected) considering shadow effects. Goal: Producatbility of concentrating power plants
  9. 9. The differential water vapour absorption in 10.8 μm and 12.0 μm channels (split window channels), allows estimation of water vapour column between surface to top of atmosphere i.e., information about water vapour content is retrieved by differential trasmittance and then differential absorption coefficient in both channels . Water vapour is one of the most important absorber in the atmosphere and strongly influence the incoming solar radiation at the surface. Inizialization of Radiative Transfer Model (RTM) TWC (Total Water Content) Mask High BT = High trasmittance = low atmospheric level observation 12.0 μm 10.8 μm Curtesy of Eumetsat Freitag 24 juli 2009
  10. 10. Thank you! Freitag 24 juli 2009