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The EU's latest Earth observer has returned its first pictures.

Sentinel-3a, which was , will have a special focus on the oceans, measuring the colour, temperature and height of sea surfaces.

The information will be invaluable to weather forecasters, and to marine biologists trying to understand the health of global waters.

The first images show the Strait of Gibraltar, the Californian coast, and an ice-covered Svalbard archipelago.

They were acquired by the spacecraft's Ocean and Land Colour Instrument, OLCI.

As the name suggests, this sensor is not solely devoted to ocean work, and will gather data about land surfaces as well, monitoring the state of vegetation across the planet, for example.

"We received the first images on 29 February, but we've had to spend a bit of time working on them to get the calibration right," said Volker Liebig, the director of Earth observation at the European Space Agency (Esa).

"We're not ready with everything onboard the satellite yet, that's clear; but we thought it important to get the pictures out there," he told 91�ȱ� News.

A few months of testing still lie ahead before the spacecraft begins routine observations.

Sentinel-3a is one in a series of satellites being procured for the .

The data from this multi-billion-euro project is expected to drive myriad applications, ranging from air quality updates to crop-performance monitoring, from water-resource management to transport infrastructure planning.

Esa acts as the technical agent, scoping the design of the satellites and then getting industry to build them.

For Sentinel-3, all the follow-on models - b, c and d - have already been contracted, meaning there should be operational continuity in orbit extending through to at least 2030.

As well as OLCI, the new satellite has a radiometer to measure the temperature of ocean and land surfaces, and an altimeter to measure ocean height.

Together, these two instruments will be useful for tracking phenomena such as El Nino, which sees warm waters bulge in the eastern Pacific every few years. The current event - one of the largest on record - has triggered a disruption in weather patterns worldwide.

It is no surprise then that are particularly keen to get their hands on Sentinel-3 data, to use in their numerical forecasting models.

"Yes, Sentinel-3 is an ocean workhorse, but it's also a global workhorse," said Esa senior scientist Dr Craig Donlon.

"The vegetation products we'll get from OLCI in 21 bands will be really excellent, so there will be a huge amount we'll get out of it just looking at land surfaces. And then there's all the work it will do measuring ice surfaces, and rivers and lakes using its altimeter," he told 91�ȱ� News.

Sentinel-3a joins two other series satellites already in orbit.

Sentinel-1a was launched in 2014 and is equipped with a radar to measure the shape of the Earth's surface; Sentinel-2a, which went up last year, has a colour camera to record how the land surface is being used and how that changes over time.

More Sentinels are coming, and the European Commission and Esa have even started to think about extending the initial suite of sensors.

There is a desire for Europe to have some kind of space-borne carbon-monitoring capability - a tool to check that countries are implementing policies to reduce emissions of carbon dioxide and other greenhouse gases.

"This would be a multi-satellite mission," said Prof Liebig.

"The idea would be to have a first prototype satellite by 2025, let's say; and then a full system around 2030. But if we want to achieve this we have to start in this (EU) financial perspective."

The European-funded Sentinel series

What is the Copernicus programme?

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: