OCRA radiometric cloud fractions for GOME-2 on MetOp-A/B
This paper describes an approach for cloud parameter retrieval (radiometric cloud-fraction estimation) using the polarization measurements of the Global Ozone Monitoring Experiment-2 (GOME-2) onboard the MetOp-A/B satellites. The core component of the Optical Cloud Recognition Algorithm (OCRA) is th...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-05-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/9/2357/2016/amt-9-2357-2016.pdf |
| Summary: | This paper describes an
approach for cloud parameter retrieval (radiometric cloud-fraction
estimation) using the polarization measurements of the Global Ozone
Monitoring Experiment-2 (GOME-2) onboard the MetOp-A/B satellites. The core
component of the Optical Cloud Recognition Algorithm (OCRA) is the
calculation of monthly cloud-free reflectances for a global grid (resolution
of 0.2° in longitude and 0.2° in latitude) to derive
radiometric cloud fractions. These cloud fractions will serve as a priori
information for the retrieval of cloud-top height (CTH), cloud-top pressure
(CTP), cloud-top albedo (CTA) and cloud optical thickness (COT) with the
Retrieval Of Cloud Information using Neural Networks (ROCINN) algorithm. This
approach is already being implemented operationally for the GOME/ERS-2 and
SCIAMACHY/ENVISAT sensors and here we present version 3.0 of the OCRA
algorithm applied to the GOME-2 sensors.<br><br>
Based on more than five years of GOME-2A data (April 2008 to June 2013),
reflectances are calculated for ≈ 35 000 orbits. For each
measurement a degradation correction as well as a viewing-angle-dependent and
latitude-dependent correction is applied. In addition, an empirical
correction scheme is introduced in order to remove the effect of oceanic sun
glint. A comparison of the GOME-2A/B OCRA cloud fractions with colocated
AVHRR (Advanced Very High Resolution Radiometer) geometrical
cloud fractions shows a general good agreement with a mean difference of
−0.15 ± 0.20.<br><br>
From an operational point of view, an advantage of the OCRA algorithm is its
very fast computational time and its straightforward transferability to
similar sensors like OMI (Ozone Monitoring Instrument), TROPOMI (TROPOspheric
Monitoring Instrument) on Sentinel 5 Precursor, as well as Sentinel 4 and
Sentinel 5.<br><br>
In conclusion, it is shown that a robust, accurate and fast radiometric cloud-fraction estimation for GOME-2 can be achieved with OCRA using
polarization measurement devices (PMDs). |
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| ISSN: | 1867-1381 1867-8548 |