Analysis of improvements in MOPITT observational coverage over Canada
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Published:2022-02-09
Issue:3
Volume:15
Page:701-719
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ISSN:1867-8548
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Container-title:Atmospheric Measurement Techniques
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language:en
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Short-container-title:Atmos. Meas. Tech.
Author:
Marey Heba S., Drummond James R., Jones Dylan B. A., Worden HelenORCID, Deeter Merritt N., Gille John, Mao Debbie
Abstract
Abstract. The Measurements of Pollution in the Troposphere (MOPITT) satellite instrument has been measuring global tropospheric carbon monoxide (CO) since March 2000, providing the longest nearly continuous record of CO from space. During its long mission, the data processing algorithms have been updated to
improve the quality of CO retrievals and the sensitivity to the lower
troposphere. Currently, MOPITT retrievals are only performed for clear-sky
observations or over low clouds for ocean scenes. The cloud detection scheme was modified in the new V9 product, resulting in an improvement in
observational coverage, especially over land. Comparison of the spatial and
seasonal variations of the data coverage in V9 and V8 shows differences with significant geographical and temporal variability, with some regions such as
Canada and the Amazon exhibiting a doubling of data in winter. Here we
conducted an analysis of Moderate Resolution Imaging Spectroradiometer
(MODIS) cloud heights and cloud mask products along with MOPITT retrieval
cloud flag descriptors to understand the impact of cloud conditions on the
MOPITT observational coverage, with a particular focus on observations over
Canada. The MOPITT CO total column (TC) data were modified by turning off
the cloud detection scheme to allow for a CO retrieval result, regardless of
their cloud status. Analyses of the standard V8 CO TC product (cloud
filtered) and non-standard product (non-cloud-masked) were conducted for
selected days. Results showed some coherent structures that were observed
frequently in the non-masked CO product that was not present in the V8
product and could potentially be actual CO features. Many times, these CO
plumes were also seen in the Infrared Atmospheric Sounding Interferometer
(IASI) CO TC product. The MODIS cloud height analysis revealed that a
significant number of low-cloud CO retrievals were discarded in the V8
product. Most of the missed CO plumes in the V8 product are now detected in
the new V9 product as a result of the dependence of the MOPITT radiance ratio
(MRT) test over land. Comparisons of the MRT and MODIS cloud height data
indicate a remarkable negative correlation. As a result of the modified V9 cloud detection algorithm, a significant portion of the low-cloud CO retrievals is now incorporated in the new V9 MOPITT product. Consequently, the observational coverage over Canada is significantly improved, which benefits
analyses of regional CO variability, especially during extreme pollution
events. We also conducted a comparison of MOPITT and IASI CO TC and found
generally good agreement, with about a 5 %–10 % positive bias that is more pronounced in highly polluted scenes.
Funder
Canadian Space Agency
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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