Coordination Group for Meteorological Satellites - CGMS Korea Meteorological Administration, May 2015 KMA Progress on COMS Cloud Detection Presented to CGMS-43 Working Group II/8

Coordination Group for Meteorological Satellites - CGMS Korea Meteorological Administration, May 2015 Contents 2 Current status of COMS cloud detection(CLD) - Problem of COMS CLD algorithm A new algorithm of cloud detection Results Future works Contents

Coordination Group for Meteorological Satellites - CGMS Korea Meteorological Administration, May 2015 Slide: 3 1. Current Status of COMS Cloud Detection Test1: Single channel reflectance Test2 : Single channel temp. test Test3 : Dual channel reflectance ratio Test4 : Temp. difference test Test5 : Homogeneity test Test6 : Sun-glint test STEP 6: Threshold test CLD Flowchart Shading : test is used applicable time, Twilling : 85 ≤ SZA ≤ 95 Cloud detection is a baseline of the 16 products through CMDPS CLD algorithm uses the conventional static thresholds method, which is composed of 7steps 4 different time zones are divided according to the solar zenith angle

Coordination Group for Meteorological Satellites - CGMS Korea Meteorological Administration, May 2015 Slide: 4 1. Problem of current COMS CLD algorithm There is discontinuity in transition area ( 85 ≤ SZA ≤95) - Visible reflectivity rapidly shrinks to high solar zenith angle - BTD(3.7-11μm) can’t be used at transition region due to the contamination of solar reflectance at the SWIR channel(3.7μm) 2. A new algorithm of cloud detection To reduce the discontinuity of cloud detection - Normalize reflectance and, - dynamic brightness temp. difference between 11 and 3.7μm are introduced

Coordination Group for Meteorological Satellites - CGMS Korea Meteorological Administration, May A new algorithm of cloud detection 5 Figure 1. Comparison of Li and Shibata (2006) and the inverse cosine factor methods for normalization of solar angle. (Dashed line: inverse cosine, solid line: represents Li and Shibata)

Coordination Group for Meteorological Satellites - CGMS Korea Meteorological Administration, May 2015 Dynamic Thresholds for BTD BTD is useful for detecting fog and low level cloud in night time because the 3.7μm is more sensitive to water droplet than 11μm. - However, brightness temperature of 3.7μm channel is rapidly increase or decrease in day/night transition zone due to solar reflection component. - For this reason, BTD has been used only at night time in operational algorithm. - Figure 2 shows dynamic threshold values of BTD in transition zone. 2. A new algorithm of cloud detection 6 Figure 2. Red lines (land) and blue dots (ocean) are dynamic threshold values of BTD with solar zenith angle.

Coordination Group for Meteorological Satellites - CGMS Korea Meteorological Administration, May Results from new CLD algorithm 7 Figure 3. Comparison of operational and modified COMS Cloud Mask on 2000 ~ 2345 UTC(0500 ~0845 KST) April 30, 2014 in the East Asia. White is cloud, blue, green and black pixel represents clear land and sea. Operational New

Coordination Group for Meteorological Satellites - CGMS Korea Meteorological Administration, May 2015 Now we are doing validation processes with MODIS cloud mask data. Then we adapt this technique to the operational COMS cloud detection algorithm for solving discontinuity in transition region. This technique will be applied to cloud detection algorithm of the next Korean geostationary meteorological satellite Geo-KOMPSAT-2A. 3. Future works 8