Introduction of the in-orbit test and its performance for the first meteorological imager of the Communication, Ocean, and Meteorological Satellite

Atmos. Meas. Tech., 7, 2471–2485, 2014 www.atmos-meas-tech.net/7/2471/2014/ doi:10.5194/amt-7-2471-2014 © Author(s) 2014. CC Attribution 3.0 License. Introduction of the in-orbit test and its performance for the first meteorological imager of the Communication, Ocean, and Meteorological Satellite D. H. Kim1 and M. H. Ahn2 1 National Meteorological Satellite Center/KMA, 64-18 Guam-gil, Gwanghyewon-myeon, Jincheon-gun, Chungcheongbuk-do, 365-830, Republic of Korea 2 Department of Atmospheric Science and Engineering, Ewha Womans University, 52 Ewhayeodae-gil, Seodaemun-gu, Seoul, 120-750, Republic of Korea Correspondence to: M. H. Ahn () Received: 13 August 2013 – Published in Atmos. Meas. Tech. Discuss.: 17 December 2013 Revised: 20 June 2014 – Accepted: 26 June 2014 – Published: 12 August 2014 Abstract. The first geostationary Earth observation satellite of Korea – the Communication, Ocean, and Meteorological Satellite (COMS) – was successfully launched on 27 June 2010. After arrival at its operational orbit, the satellite underwent an in-orbit test (IOT) that lasted for about 8 months. During the IOT period, the main payload for the weather application, the meteorological imager, went through successful tests for demonstrating its function and performance, and the test results are introduced here. The radiometric performance of the meteorological imager (MI) is tested by means of signal-to-noise ratio (SNR) for the visible channel, noise-equivalent differential temperature (NEdT) for the infrared channels, and pixel-to-pixel nonuniformity for both the visible and infrared channels. In the case of the visible channel, the SNR of all eight detectors is obtained using the ground-measured parameters with the background signals obtained in orbit. The overall performance shows a value larger than 26 at 5 % albedo, exceeding the user requirement of 10 by a significant margin. Also, the relative variability of detector responsivity among the eight visible channels meets the user requirement, showing values within 10 % of the user requirement. For the infrared channels, the NEdT of each detector is well within the user requirement and is comparable with or better than the legacy instruments, except for the water vapor channel, which is slightly noisier than the legacy instruments. The variability of detector responsivity of infrared channels is also below the user requirement, within 40 % of the requirement, except for the shortwave infrared channel. The improved performance result is partly due to the stable and low detector temperature obtained due to spacecraft design, i.e., by installing a single solar panel on the opposite side of the MI. 1 Introduction Geostationary meteorological satellites have played important roles as storm trackers, a global source of important geophysical information such as sea surface temperature, and providers of long-term records for climatic applications (Purdom and Menzel, 1996; Schmetz et al., 2002). The current constellation of six geostationary satellites (GOES-W and GOES-E, MTSAT, FY-2, Meteosat, and Meteosat Indian Ocean) meets the basic requirements – a geostationary image at least twice an hour – although better temporal resolution is required for rapidly changing phenomena such as tropical cyclones. Furthermore, backup satellites for contingency situations are quite important to ensure the continuity of operational weather satellites (CGMS, 2007). In such situations, a new geostationary satellite capable of operational meteorological observation could play an important role. The first multi-purpose geostationary observation satellite of Korea, COMS (Communication, Ocean, and Meteorological Satellite), is such an addition. COMS, successfully launched on 27 June 2010, is designed to perform three major missions, including operational weather observation along Published by Copernicus Publications on behalf of the European Geosciences Union. 2472 D. H. Kim and M. H. Ahn: In-orbit test results of COMS/MI Figure 1. Comparison of the spectral response function (SRF) of COMS/MI with other legacy instruments onboard GOES-13/-15 and MTSAT-2 satellites. with oceanography observation and space proofing of a Kaband transponder. The main payload for weather observation is the meteorological imager (MI), an imaging radiometer with the five observation channels, one in the visible band (VIS), one in shortwave infrared band (SWIR), one in the water vapor absorption band (WV), and two split window bands (IR1 and IR2). Figure 1 and Table 1 summarize the spectral response functions (SRFs) and the channel specifications, respectively. A more detailed description of COMS/MI is found in Appendix A1. The COMS program has a few differences that stand out from legacy programs. For example, the planned mission lifetime of COMS is longer than that of usual geostationary meteorological satellite missions: 7 years versus 5 years. Also, the spacecraft is designed to provide the least interference with MI performance, especially for the infrared channels, due to it having a single solar panel without the balancing structure used for the previous GOES series or MTSAT series (Menzel and Purdom, 1994; SS/Loral, 1996). Thus, instrument characterization during the ground tests and the in-orbit test (IOT) performed after the launch are quite important for the new system and will play an important role in ensuring the longer mission lifetime. Here, we introduce the IOT procedures as well as the important outputs for the main meteorological payload, in terms of its functional and radiometric performances. Section 2 briefly summarizes the IOT procedures and results, followed by the characteristics of the radiometric performance of COMS/MI in Sect. 3. Section 4 summarizes the performance characteristics obtained during the IOT and concludes the paper. 2 In-orbit test (IOT) Here, we introduce the activities and major outcomes from the IOT, started soon after COMS’ arrival at the service orbit, 128.2◦ E. The major goals for the IOT were to make sure that COMS and its payloads have survived the launch, to demonstrate that the performance in space is in line with the predicted performance, and to collect information and data Atmos. Meas. Tech., 7, 2471–2485, 2014 Figure 2. The first visible images of COMS/MI taken on 12 July 2010. (a) is the original 1.75 oversampled image and (b) is the rectified image. for the actual operation of satellite, as well as fine tuning of equipment and algorithms. The IOT activities can be categorized into the activities for the system and payload checks, the functional and performance tests, and preparation for operation. While a detailed description for the IOT is provided in Appendix A2, several interesting activities such as the acquisition of the first image, a successful outgassing operation, and the beginning of the full test are introduced here. The first COMS/MI image is taken from 02:15 UTC to 02:45 UTC on 12 July 2010, on (...truncated)