ADEOS: combine instruments without losing their identities

The Advanced Earth Observing Satellite, ADEOS, also called Midori, launched in 1996. Its successor ADEOS-II, or Midori II (Midori-2 in the archive), launched in December 2002. They carried instruments intended to examine different parts of the environment, with international participation. Their shared scientific ambition was to connect observations of Earth’s oceans, land and atmosphere. The two spacecraft remain separate missions even when they are discussed as one development lineage.

A multi-instrument platform can provide related observations from a common orbit, but each sensor retains its own response and footprint. Combining them requires a clear connection between the physical quantities being inferred. A water-cycle question might use microwave information alongside cloud and surface observations. Placing several sensors on one spacecraft does not automatically turn every measurement into the same kind of map.

The NASA Scatterometer, NSCAT, flew on the first ADEOS. SeaWinds flew on ADEOS-II, which also carried instruments including the Advanced Microwave Scanning Radiometer — open definition and Global Imager. A scatterometer transmits radar pulses and measures the ocean’s returned signal from different viewing directions. Wind-generated surface roughness affects that signal, allowing a model to estimate near-surface wind speed and direction. It is not a direct photograph of invisible moving air.

A passive microwave radiometer instead measures incoming radiation in its observing bands. Those measurements support different retrievals and do not make it the same instrument as SeaWinds. Suppose a fictional ocean study combines a wind product with a water-related product. The analyst must check their times, footprints and assumptions before arguing that one pattern explains the other. Sharing the spacecraft does not guarantee that every product samples exactly the same place in exactly the same way.

One platform, different measurements

Both missions ended earlier than planned. The first ADEOS lost power in 1997 after a solar-array blanket failure. ADEOS-II stopped communicating following an anomaly in October 2003, and recovery was judged extremely unlikely. The lesson does not infer that both failures had an identical mechanism. A shared reliance on spacecraft power explains why payload health alone cannot guarantee continued observations.

A shortened mission can still produce useful data, but it changes which scientific questions its record can support. Several months of observations may document seasonal events without establishing a multi-decade climate trend on their own. Researchers can combine compatible records from other missions, with appropriate calibration and uncertainty. Evaluate both the measurements obtained and the missing coverage instead of equating an incomplete lifetime with either no value or complete success.