Introduction

This page provides an overview of the work performed at the University of Oxford and the Rutherford Appleton Laboratory on the Oxford-RAL Retrieval of Aerosol and Cloud (ORAC) algorithm. The project is lead by Dr R.G. Grainger of the University of Oxford.

Algorithm

The Oxford-RAL Retrieval of Aerosol and Cloudis an optimal estimation scheme that determines aerosol and cloud properties from multispectral imagery [Thomas et al., 2010a,b, Poulsen et al., in press, Sayer et al., 2011]. The scheme uses Discrete Ordinates Radiative Transfer (DISORT) [Stammes et al., 1988] to model the top of atmosphere radiance as a function of the properties of a plane parallel cloud layer or aerosol with an assumed height distribution. The optimal estimation framework fits the radiance in all channels by varying all retrieved parameters simultaneously, while taking a priori information into account. The scheme also provides error estimates on all retrieved quantities.

The code has been applied to measurements by ATSR-2, AATSR and MSG-SEVIRI. The following is a description of the ATSR-2 nadir view retrieval. Cloud properties are retrieved using the 0.67, 0.87, 1.6, 11 and 12 µm channels and the derived products are optical depth at 0.55 µm, effective radius, liquid water path, cloud top height, pressure and temperature and the fraction of each pixel filled with cloud. Aerosol properties are retrieved using the 0.67, 0.87 and 1.6 µm channels and the products are 0.55 µm optical depth and effective radius.

Product Availability

Funding

• National Centre for Earth Observation: Atmospheric Composition Theme
• ADIENT
  
• Globaerosol(Completed)
  
• SEVIRI Observations of Saharan Dust(Completed)
  
• Quantify (Ship Tracks, Completed)
  
• ADRIEX (Completed)
  
• EUMETSAT Aerosol (Completed)
  
• GRAPE (Completed)
  

ORAC Meeting Dates for 2011

Maintained by Don Grainger