A passive and active L-band microwave sensor, Aquarius, developed by NASA to observe the global sea surface salinity
(SSS) distribution, was launched on 10 June 2011. The SSS observed by Aquarius (v.1.3) was evaluated by comparison
with in-situ salinity data from various sources. The Aquarius SSS generally agreed well with salinity measurements by
Argo floats in moderate to high sea surface temperature (SST) regions. However, the Aquarius SSS highly deviated in
low SST and high wind regions. Typical root-mean-squared difference between the Aquarius and in situ SSS
observations under a condition of sea surface temperature higher than 5°C were 0.7 psu for snapshot observations and
0.35~0.4 psu for monthly 1° x 1° averages.
Japan Aerospace Exploration Agency (JAXA) is proposing the Global Change Observation Mission (GCOM). The GCOM mission will take over the Advanced Earth Observing Satellite-II (ADEOS-II or Midori-II) mission and develop into long-term monitoring. The GCOM mission will consist of two series of medium size satellites: GCOM-W and GCOM-C (these names are provisional). Three consecutive generations of satellites with one year overlap will result in over 13 years observing period in total. Two observing instruments are proposed for the GCOM-W satellite: the Advanced Microwave Scanning Radiometer (AMSR) follow-on instrument and hopefully the scatterometer for measuring ocean vector winds like SeaWinds onboard Midori-II. To keep the continuous observation by AMSR-E on Aqua, the earliest launch date is desired by science community. Current proposed launch year is 2010. The AMSR follow-on instrument will be a multi frequency, dual polarized passive microwave radiometer that observes water-related geophysical parameters supporting the GCOM concept. To keep the earliest launch date, only minimum but essential modifications from AMSR-E are now being examined. Combination of AMSR follow-on instrument and the scatterometer will provide unique opportunity to generate a synergistic effect of the active and passive microwave measurement. This combination can provide some instrument-level advantages including attenuation and scattering correction for scatterometer. Furthermore, simultaneous measurements of water vapor, SST, precipitation, and sea surface winds are effective for investigating various time-space scale phenomena.