Landsat satellites are undoubtedly the best known and most used source of imagery. They commenced operation in the 1970s and are still in use today.
Landsat data continuity is vitally important. Its 30 plus years of data lets scientists assess the impact of human activity on the land.
Recently, the continuity of the Landsat program has been an issue. The US government has been unsuccessful in its attempt to commercialise the program. Moreover, in May 2003, when the scan line corrector on Landsat-7 unexpectedly failed, the risk to the continuity of data supply was highlighted.
Although a number of countries now operate remote sensing satellites, none of them is comparable to the Landsat program in terms of accessibility and distribution policy.
Its spatial and spectral characteristics are uniquely designed to support a wide range of applications. The program is cost effective, and its users are familiar with it. Moreover, the users have come to depend on it for operational projects in mapping and monitoring.
Today, a number of important projects depend on data from Landsat. At a federal level, the Australian Greenhouse Office has used those 30 years of Landsat data to create land cover change maps, in support of a national system for carbon accounting. Since 1997, Geoscience Australia has been using the data to update its national topographic maps.
It offers 30 plus years of continuous earth observation data ...
Landsat has been used for Queensland's State Landcover and Trees Study program and for Western Australia's Feed-On Offer and Land Monitor projects. In South Australia, people use it to monitor vegetation clearing
Australia is one of the few OECD countries that neither operates remote-sensing satellites by itself nor with a consortium. The situation is unlikely to change in the near future. The next best option is to work in partnership with other space agencies to ensure the country has access to good satellite data.
The Australian Centre for Remote Sensing (ACRES) was established in 1979 and operates within Geoscience Australia for just this purpose. It is responsible for acquiring and distributing Landsat data in Australia.
In that role, ACRES has been developing strategies for ensuring data continuity by building on it's strategic relationship with US government agencies. The centre has adopted a number of approaches to ensure that Australian users have continued access to the data.
It is the most stable remote sensing satellite ever launched ...
In the short term, ACRES is processing Landsat-5 and Landsat-7 imagery for maximum utility.
Despite recent problems encountered with Landsat 7, it remains the best calibrated, most stable remote sensing satellite ever launched.
Although the US Geological Survey acknowledges that the data has been affected due to the loss of the scan line corrector, it says that some 75 per cent of the data's utility remains. In an existing ACRES project, composite products of contemporary SLC-off scenes and SLC-on scenes obtained a year earlier will be provided.
Starting early next year, composite scenes will be obtained by merging SLC-off scenes from sequential orbits, so much of the lost utility should be restored.
Although Landsat-5 recently had its 20th anniversary, it continues to perform well. A recent transmitter problem has been solved, and some 12 stations are now taking the Landsat-5 downlink.
On 5 August, NASA issued a new request for information about the Landsat Data Continuity Mission. In the document, NASA asks for comments about various options for continued Landsat-like data observations now being considered by the US Government.
One of the options is to migrate the Landsat instrument to the National Polar-orbiting Operational Environmental Satellite System, which is to be launched in 2009. In the interim, a proposal has been put to launch a bridge mission to minimise the risk to Landsat-data continuity.
An interagency group consisting of NASA, USGS, NOAA and NGA is currently working out the details of this proposal.
In 2003, Geoscience Australia and the USGS signed an agreement to extend the two agencies' co-operation. Under the agreement, ACRES has become part of the USGS Landsat network station.
ACRES is the only station located outside the US that has this function. In this role, telemetry data from Landsat satellites is provided in real time to the operations centre at the Goddard Space Flight Centre. The information is used to monitor the spacecraft's health.
ACRES is the only station outside the US to have this function ...
Finally, a contingency plan is being developed in case Landsat fails. Other imagery sources are being investigated, and although at present no imagery source has all Landsat's characteristics and benefits, alternatives exist.
For the moment, though, scientists are continuing to use Landsat to provide users with useful imagery. At the same time, a concerted effort is being made to ensure that the heritage of Landsat data is available to benefit the public far into the future.
The authors are with the Australian Centre for Remote Sensing, a business unit of Geoscience Australia
