<title>MOPITT cloud detection and its validation</title>

Abstract

ABSTRACT The measurements of Pollution in the Troposphere (MOPITT) instrument aboard the Earth ObservingSystem (EOS) Terra spacecraft measures tropospheric CO and CH 4 by use of a nadir-viewing geometry.MOPITT cloud algorithm detects and removes measurements contaminated by clouds before retrieving COprofiles and CO and CH 4 total columns. The collocation between MOPITT and MODIS is also establishedand MODIS cloud mask will be used in the MOPITT cloud algorithm. The cloud detection results in theuse of MOPITT data alone agree with MODIS cloud mask for more than 80% of the tested cases.Keywords: MOPITT, cloud detection, tropospheric CO, CH4 1. INTRODUCTION The Measurement Of Pollution In The Troposphere (MOPITT) instrument on board EOS Terra is designedto measure the tropospheric CO and CH 4 at a nadir-viewing geometry. The measurements are taken at4.7um in the thermal region, and 2.3um and 2.2um in the solar region for CO mixing ratio retrieval, COtotal column amount and CH 4 column amount retrieval, respectively. To ensure the required measurementaccuracy, it is critical to identify and remove any cloud contamination to the channel signals. In this study,we develop an algorithm to detect the cloudy pixels by comparing the observed thermal radiance with themodel calculated clear sky radiance and by estimating cloud top pressures using CH