CGMS-41 CMA-WP-09 Prepared by CMA Agenda Item: III/2 Discussed in WG III

STATUS OF INVESTIGATION ON USING EARLY MORNING ORBIT BY FY-3

Executive summary

Current polar satellites being on-orbit include NOAA-15/16/18/19, NPP, METOP-A/B and FY-3A/B. In view of the coverage by FY-3A/B、NPP and METOP-B，gaps obviously exist for the current global operational polar-orbiting constellation. Early morning orbit shall mitigate the problem; as a result, improvement in numerical weather prediction is anticipated among all possible benefits, for instance, to the tropical cyclone monitoring with infrared and microwave imagery and sounding, fog and fire detection, air quality monitoring, improved sampling of diurnal cycle for climate data records, and to the quasi-continuous monitoring of the sun for space weather and climate applications.

In response to CGMS Recommendation 39.01 that invites agencies to assess the possibility of implementing an IR Sounding in early morning orbit, CMA presented a report ‘CMA Consideration on early-morning orbit satellite’ by Yang Jun at CGMS40 in Lugano. The report made a preliminary feasibility analysis of redeploying an FY-3 mission from e.g. a mid-morning orbit to the early morning. After CGMS-40, CMA hosted or organized several discussions to further investigate the issue. According to the investigation results，CMA has tentatively figured out a priority payload configuration for the FY-3 early morning orbit, that includes low-light level channel, MWTS, MWHS, WindRAD、HIRAS、GNOS and Space Environment Suite.

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Status of Investigation

on Using Early Morning Orbit by FY-3

1 ON-ORBIT POLAR SATELLITES

Currently, polar satellites being on-orbit include NOAA-15/16/18/19, NPP, METOP-A/B and FY-3A/B. NOAA mainly operated PM satellite. NOAA-15 is operated as AM secondary, NOAA-16/18 is operated as PM secondary option, and NOAA-19 is currently operated as PM primary option. In the future, NPP will take the primary place instead of NOAA-19, and EUMETSAT operates METOP-B and METOP-A as the AM primary and backup option. In view of the space coverage of FY-3A/B, NPP and METOP-B，gaps obviously exist in the world operational polar-orbiting constellation.

Fig.1 Gaps obviously exist in current operational polar- orbiting constellation.

2 FY-3 POLAR SATELLITES PLAN

2.1 Tentative Schedule for Future FY LEO Series

For the Fengyun LEO satellites, after FY-3A/B, the future FY-3 models (FY-3C/D/E/F) have been approved. CMA plans to develop certain observational capabilities for the follow-up models, for instance, the WindRAD for sea winds, the GAS for greenhouse gases absorption measurement. The atmospheric sounding shall be enhanced by replacing the current IRAS with HIRAS (Hyper-spectral Infra-red Atmospheric Sounder), and by the deployment of radio occultation sounder GNOS. Also, there is a plan to develop rainfall measurement satellite: FY-3RM, that shall carry Ku/Ka band radar, microwave sounding and imaging instruments.

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Table 1 Tentative Schedule for Future FY Series

LEO. Schedule FY-3

2013 Operational (A.M. Orbit) 2014 Operational (P.M. Orbit)

2015 2016 Operational (A.M. Orbit) 2017 2018 Operational (P.M. Orbit) 2019 Operational (Rain Fall Mission) 2020 Operational (A.M. Orbit)

Table2. FY-3C/D/E/F Payload Configuration

3 LATEST PROGRESS

In response to CGMS Recommendation 39.01 that invited CGMS agencies to assess the possibility of implementing an IR Sounding in early morning orbit, CMA made a presentation t ‘CMA Consideration on early-morning orbit satellite’ by Yang Jun at CGMS40 in Lugano. The

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presentation made a preliminary feasibility analysis of redeploying an FY-3 mission from e.g. a mid-morning orbit to the early morning. CMA indicated its willingness to investigate the possibility of flying the mission with sounding capabilities in the early-morning orbit in order to have a better distribution of atmospheric sounding system over the planned 3 orbits. After CGMS-40, CMA hosted, or organized several discussions about the issue. A seminar was convened on 25 and 26 April in Beijing to perform a critical analysis of the results of the various impact studies conducted by the WMO Tiger Team. The seminar was informed of the activities by CMA and the Shanghai Academy of Spaceflight Technology (SAST), including further investigation on payload configuration, modification and accommodation for a potential early morning orbit mission, as well as user workshops to solicit users’ advice and opinion nation wide. At the April’s seminar chaired by the WMO Secretariat representative, the Tiger Team confirmed that the early morning orbit satellite observation has positive contribution to global NWP. Besides global NWP, benefit are recognized for synchronisation with the daily meteorological briefing (8am/8pm), for tropical cyclone monitoring, for better temporal sampling of diurnal cycle for climate monitoring, for air quality monitoring, fog and fire detection, and for the solar observations.

3.1 Feasibility Study on FY-3 Use of Early Morning Orbit FY-3 series serves at least for another 15 years with the additional four satellites. 16

improved or new instruments will be configured on FY-3C/D/E/F. It is unrealistic for CMA to fly three orbits (AM, PM, and Early Morning) at the same time. Since FY-3C & 3D are being manufactured now, there is no chance to make them changed for the Early Morning orbit. FY-3E is possibly the only opportunity for CMA to fly early morning orbit before 2020.

3.2 Latest Progress The potential user workshops have been called up twice to assess the requirements at the

national level. Four engineering feasibility seminars have been held by CMA and SAST to investigate payload and platform adaptation needed to fly a FY-3 satellite in the early morning orbit, as well as the actions needed to secure a launch by 2016, as it’s anticipated. The financial support discussions were also held in Jan 2013. On 25 and 26 April in Beijing, a seminar was convened at invitation of CMA that performed a critical analysis of the results from various impact studies conducted by the WMO Tiger Team.

3.3 Payload and Orbit Options

3.3.1 Payload Specifications According to the results of potential user workshop, engineering feasibility studies,

Financial Support Discussion and Tiger Team seminar，tentatively, CMA has figured out a priority payload configuration of the FY-3 early morning orbit, which includes low light level channel, MWTS, MWHS, WindRAD、HIRAS、GNOS and space environment Suite.

Table 3 Instruments of FY-3 early morning orbit

Table 3.1 HIRAS details Acronym HIRAS

Full name Hyperspectral Infrared Atmospheric Sounder

Type of Instrument Cross-nadir scanning IR sounder

Purpose Temperature/humidity sounding, ozone profile and total-column green-house gases

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Short description Michelson interferometer with three bands

Background Replacing IRAS on FY 3A, 3B and 3C

Scanning Technique 58 pixels / scan line, arranged in 2 x 2 arrays; swath 2250 km

Resolution 1.1 degree (16 km) IFOV

Coverage / Cycle Near-global, twice/day

Mass 120 kg Power 129 W Data Rate

Table 3.2 MWHS details Acronym MWHS

Full name Micro-Wave Humidity Sounder

Type of Instrument MW sounding radiometer, cross-track scanning

Purpose Humidity sounding in nearly-all-weather conditions. Also, precipitation

Short description 15 frequencies including bands 183 GHz (for humidity), and 118 GHz (for supporting information on temperature). 17 channels (dual polarisations for the two window channels)

Background Replacing the MWHS of FY-3A and FY-3B

Scanning Technique Cross-track: 98 steps of 16 km s.s.p., swath 2700 km

Resolution Window channels and band 118 GHz: 32 km at s.s.p.; band 183 GHz: 16 km at s.s.p.

Coverage / Cycle Global coverage twice/day

Table 3.3 MWTS details Acronym MWTS

Full name Micro-Wave Temperature Sounder

Type of Instrument MW sounding radiometer, cross-track scanning

Purpose Temperature sounding in nearly-all-weather conditions

Short description 13 frequencies, 13 channels

Background Evolution of MWTS flown on FY 3A and 3B

Scanning Technique Cross-track: 30 steps of 32 km s.s.p., swath 2250 km

Resolution 32 km at s.s.p.

Coverage / Cycle Near-global coverage twice/day

Table 3.4 WindRAD details Acronym WindRAD

Full name Wind Radar

Type of Instrument Radar scatterometer

Purpose Sea surface wind, surface soil moisture

Short description Two frequencies, C-band (5.3 GHz) and Ku-band (13.265 GHz). Four antennas with

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HH and VV for both frequencies. Each pixel illuminated under several viewing angles.

Background New development

Scanning Technique Conical scanning with incidence angles 36-45° (C-band) and 37-43° (Ku-band). Swath > 1200 km.

Resolution C-band: 20 km, Ku-band: 10 km

Coverage / Cycle Near-global coverage each day.

Table 3.5 GNOS details Acronym GNOS

Full name GNSS Radio Occultation Sounder

Type of Instrument GNSS radio-occultation sounder

Purpose Temperature/humidity sounding with highest vertical resolution; also space weather

Short description Measuring the phase delay due to refraction during occultation between GPS and LEO

Background Consolidated technology

Scanning Technique Limb scanning from the satellite altitude to close-to-surface by time sampling - Azimuth: 90° sectors fore- and aft-

Resolution About 300 km horizontal, 0.5 km vertical

Coverage / Cycle 2 GNSS constellations tracked. About 500 soundings/day - Average spacing 1000 km - Global coverage (300 km spacing) in 10 days

3.3.2 Orbit Options Recognizing that global even distribution of sounding data is of great significance for the 6

hour NWP assimilation window, one approach is to constitute a three orbital fleet including Metop（Mid. Morning）+ NPP(Afternoon) + FY-3(Early Morning). Three orbit satellites (METOP, NPP and FY-3EM) data coverage is nearly 100%.

Fig.2 Orbit Option: FY-3 Early Morning + NPP + Metop

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4 CONCLUSIONS AND RECOMMENDATIONS Currently, FY-3A/B is operated as AM/PM satellites. FY-3C is also an AM satellite which

will be launched later this year. Before redeploying FY-3 to an early morning orbit, CMA needs to evaluate the satellite data acquisition from EUMETSAT in the mid-morning and with USA in the afternoon. CMA also needs to find out the solutions to the satellite data applications and the impact on the CMA operational system. From the point of improving global numerical weather prediction, CMA is considering starting the procedure for redeploying FY3 to an early morning orbit and calls on support from WMO, CGMS members and satellite operators to reach this objective. It is essential to ensure that data from the three orbits continue to be shared between satellite operators. International effort is needed to support trade-off studies (including e.g. OSSEs) necessary in the course of the development phase of the FY-3 early morning mission. International partners are requested to pursue stronger collaboration as soon as possible for data assimilation, in order to maximize the benefits of future (early morning) and current FY-3 missions. Other supports for the early morning orbit polar satellite data applications, such as space weather, climate monitoring, air quality and disaster monitoring, are also needed from the international community.

CMA will continue to investigate the possibility of flying the mission with sounding capabilities in the early-morning orbit in order to have a better distribution of atmospheric sounding system over the planned 3 orbits and to improve the global numerical weather prediction.