Ocean Colour Cubes

August 2009 Monthly Chlorophyll-a Composite; data courtesy of the ESA Ocean Colour Climate Change Initiative project

August 2009 Monthly Chlorophyll-a Composite; data courtesy of the ESA Ocean Colour Climate Change Initiative project

It’s an exciting time to be in ocean colour! A couple of weeks ago we highlighted the new US partnership using ocean colour as an early warning system for harmful freshwater algae blooms, and last week a new ocean colour CubeSat development was announced.

Ocean colour is something very close to our heart; it was the basis of Sam’s PhD and a field of research she is highly active in today. When Sam began studying her PhD, Coastal Zone Color Scanner (CZCS) was the main source of satellite ocean colour data, until it was superseded by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) that became the focus of her role at Plymouth Marine Laboratory.

Currently, there are a number ocean colour instruments in orbit:

  • NASA’s twin MODIS instruments on the Terra and Aqua satellites
  • NOAA’s Visible Infrared Imager Radiometer Suite (VIIRS)
  • China’s Medium Resolution Spectral Imager (MERSI), Chinese Ocean Colour and Temperature Scanner (COCTS) and Coastal Zone Imager (CZI) onboard several satellites
  • South Korea’s Geostationary Ocean Color Imager (GOCI)
  • India’s Ocean Colour Monitor on-board Oceansat-2

Despite having these instruments in orbit, there is very limited global ocean colour data available for research applications. This is because the Chinese data is not easily accessible outside China, Oceansat-2 data isn’t of sufficient quality for climate research and GOCI is a geostationary satellite so the data is only for a limited geographical area focussed on South Korea. With MODIS, the Terra satellite has limited ocean colour applications due to issues with its mirror and hence calibration; and recently the calibration on Aqua has also become unstable due to its age. Therefore, the ocean colour community is just left with VIIRS; and the data from this instrument has only been recently proved.

With limited good quality ocean colour data, there is significant concern over the potential loss of continuity in this valuable dataset. The next planned instrument to provide a global dataset will be OLCI onboard ESA’s Sentinel 3A, due to be launched in November 2015; with everyone having their fingers crossed that MODIS will hang on until then.

Launching a satellite takes time and money, and satellites carrying ocean colour sensors have generally been big, for example, Sentinel 3A weighs 1250 kg and MODIS 228.7 kg. This is why the project was announced last week to build two Ocean Colour CubeSats is so exciting; they are planned to weigh only 4 kg which reduces both the expense and the launch lead time.

The project, called SOCON (Sustained Ocean Observation from Nanosatellites), will see Clyde Space, from Glasgow in the UK, will build an initial two prototype SeaHawk CubeSats with HawkEye Ocean Colour Sensors, with a ground resolution of between 75 m and 150 m per pixel to be launched in early 2017. The project consortium includes the University of North Carolina, NASA’s Goddard Space Flight Centre, Hawk Institute for Space Sciences and Cloudland Instruments. The eventual aim is to have constellations of CubeSats providing a global view of both ocean and inland waters.

There are a number of other planned ocean colour satellite launches in the next ten years including following on missions such as Oceansat-3, two missions from China, GOCI 2, and a second VIIRS mission.

With new missions, new data applications and miniaturised technology, we could be entering a purple patch for ocean colour data – although purple in ocean colour usually represents a Chlorophyll-a concentration of around 0.01 mg/m3 on the standard SeaWiFS colour palette as shown on the image at the top of the page.

We’re truly excited and looking forward to research, products and services this golden age may offer.

Random Numbers from Space

The concept of randomness, and creation of random numbers, has been part of human culture for thousands of years; in fifth century Athens, they considered elections undemocratic, everyone was considered equal and they selected people at random from the population to serve as the government. Perhaps our current politicians should take note, although the principle itself still exists in the UK through jury duty selection.

Random numbers are integral to modern society, from the obvious betting and gambling arenas, to sport, science, the arts and cryptography – all those little devices used to log into bank accounts are based on random numbers; in addition, they’re key to satellite communication systems.

Computerised random number generators have been around as long as programmers have programmed, and their algorithms produce a series of numbers that look random, but in fact they aren’t as they have a predetermined sequence. These are known as pseudo random numbers and are fine for many uses, but aren’t suitable to applications like secure communications or cryptography; for these we need to create true random numbers.

Lightning, Copyright: Taiga / 123RF Stock Photo

Lightning, Copyright: Taiga / 123RF Stock Photo

A true random number is one whose outcome is unpredictable, for example rolling a dice. Whilst this works for a single true random number, what if you want thousands or millions? Building a machine to throw millions of dice simultaneously isn’t sensible, instead random numbers are created using a physical property of the environment applied through a computer, for example decays in radioactive sources, snapshots of lava lamps or atmospheric noise caused by lightning strikes within thunderstorms. Last Thursday night would have been a goldmine to anyone using this methodology, as over 3,000 lightning strikes hit the country within three hours.

The space sector is now becoming involved in this area. In last week’s blog we reported on the two UK satellites recently launched; the UKube-1, built by Clyde Space in Glasgow, carries a true random number generator. The JANUS experiment will test the feasibility of using cosmic radiation to create true random numbers by detecting impacts from space particles through the single event upset effect methodology.

This could offer an alternative method of creating high volumes of random numbers for the communication and cryptography industries particularly, and gives one more way in which space can help.

Blog written in conjunction with Adam Mrozek, work placement student.