From the moment Malaysian Airlines flight MH370 disappeared, I was asked the same question over and over: can satellites help find the crash site?

Immediately after the disappearance of flight MH370, several governments launched a massive search operation using satellite imagery, search aircraft and naval vessels.

Geoscience Australia supported the search efforts by undertaking the largest marine survey, mapping the seafloor in greater detail than ever to provide scientific insights.

Satellites have a large footprint and they can cover large amounts of area in short amounts of time.

If search teams had noticed objects of interest in the satellite imagery, the next task would have been to deploy air and sea resources to confirm the sightings.

Satellite imagery provides the starting point – a useful place to gather compelling evidence.

So what can these commercial satellites ‘see’?

There are two kinds of satellites which can be used in the search for debris in the ocean – optical satellites and radar satellites.

Making the assumption that the plane had actually crashed in the search area, it would have been likely that parts of the plane would be scattered and floating on the ocean surface.

Optical and radar satellites would see the floating objects slightly differently.

As you can probably determine from its name, an optical satellite can take images – or photos – of the Earth as it orbits.

Some optical satellites can see objects as small as 0.5m in size, while for others the objects must be larger to detect – say in the order of 5-10m.

The wingspan of a Boeing 777 is just over 60m. If it had still mostly been intact, and floating, then the satellite with a 0.5m ‘lens’ would be able to spot it without too much difficulty. If that was the case and there were identifiable letters on the wing, those could even have been identified in the image.

If the satellite lens was ‘10m’ then the wingspan would appear just as a collection of 5–6 dots on the image and would therefore have been harder to accurately pinpoint.

Optical satellites are good at picking up the colour, shape and size of objects – even large letters or writing on objects – but they cannot ‘see’ at night.

Radar satellites, on the other hand, would pick up reflections from the metallic part of the plane and pick up damping of the water surface due to an oil-slick. Even if the object was only a metre in length, it would appear as a bright blob on the radar imagery, assisting the analyst in tracking it.

These radar satellites will determine if there are objects in an area, but cannot reveal many details about them.

Neither can identify debris more than half a metre under the surface – at best.

Realistically, those involved in the search effort needed to closely co-ordinate the data gathering and analysis effort from both optical and radar satellites data to make the most of the imagery.

Naturally the question was asked as to why the satellite images had not been able to pinpoint the debris even after so many weeks.

One of the first issues with satellites is many of them are not looking at the same area of the Earth‘s surface all the time. At best, a satellite may fly over the area once a day. Some satellites would fly over the search area once every few days.

Of course, a big challenge with mapping debris in the open ocean is that it is always in motion – currents, winds and other environmental factors. If the debris was on a land surface it would be static and satellites could centre in a particular area, which is not possible for drifting debris.

So even if an image had clearly identified MH370 debris, the next time imagery was acquired – in a day or two – it would have moved to another point in the ocean.

Like the photos we take with our cameras, optical satellite images are snapshot in time. If the area is covered with cloud, of course we cannot take the picture and the opportunity is missed.

The very first sightings of debris reported in the media were from optical satellites called Worldview (US) and Gaofen (China).

I believe there would have been several attempts to take further pictures but cloud cover could have been a problem or potentially the debris would have drifted to another part of the ocean and the satellite would have to look at another location quite far from the original.

Radar satellites can ‘see’ through the clouds and the third reported sighting was believed to be using a German radar satellite (Germany) operated by a French company.

But again, the sightings only constituted the first key steps of the search, and the images needed to be verified.

In 2017, Australia released satellite images showing 12 “probably man-made” objects floating in the sea near the suspected crash site. The location of the images suggests that the aircraft may have crashed further north of the area that teams spent two-and-a-half years searching.

Geoscience Australia also released a public Story Map that revealed data gathered during the search.

(A version of this article was originally published in March 2014, two weeks after flight MH370 went missing.)

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