Australian Centre for Remote Sensing, AUSLIG
PO Box 2 Belconnen ACT 2616
Phone (02) 6201 4130 Fax (02) 6201 4240
The Australian Centre for Remote Sensing (ACRES) has recently introduced a new service to provide satellite data for near real time applications. The STAR (Speedy Transmission After Reception) service provides access to digital satellite data products in full resolution or compressed format within twelve hours of a satellite overpass. This service incorporates programming future satellite data acquisition, transmission of data from the ground stations to the processing facility in Canberra via a high-speed communication link and high priority processing. The introduction of this service makes it possible for ACRES to provide satellite data for time-critical applications like crop yield modelling, pre-harvest crop production forecasting, detecting and monitoring crop stress, monitoring pest infestation, floods, fires and oil-spills. SPOT-LITE is a low-cost, off-the-shelf satellite data product from ACRES that is ideal for use in a Geographical Information System (GIS) environment. SPOT-LITE can be accessed at any time via the Internet and is available in the form of tiles covering most of Australia. This paper describes case studies using the STAR service, its potential benefits for time-sensitive agricultural applications and the characteristics of SPOT-LITE, which make it ideal for GIS-based applications.
The Australian Centre for Remote Sensing (ACRES) is a business unit of the Australian Surveying and Land Information Group (AUSLIG), Department of Industry, Science and Resources. The primary functions of ACRES are to acquire, catalogue, archive, process and distribute remotely sensed data acquired from earth observation satellites for both scientific and operational applications. A number of earth observing missions including satellites like Landsat 3,4,5 and 7, SPOT 1,2,3, and 4, ERS 1 and 2, JERS 1, RADARSAT 1, NOAA and more recently Terra and EO-1 are supported by ACRES.
To achieve its objectives, ACRES operates data acquisition facilities in Alice Springs & Hobart and the Data Processing Facility (DPF) in Canberra. The data acquisition facilities at Alice Springs and Hobart consist of a steerable antenna, signal processing, cataloguing and archiving system. The Alice Springs ground station covers Australia, East Timor, parts of Indonesia and Papua New Guinea. The Hobart ground station provides coverage of New Zealand, the Southern Ocean and the edge of Antarctica.
The DPF in Canberra processes data received from the acquisition facilities to generate products for the remote sensing user community and maintains an archive of satellite data.
Satellite data - the need for speed
There is an increasing demand from satellite data users to have access to Near Real Time (NRT) information that is crucial for many emergency applications like bushfires, floods and oil spills. The availability of NRT satellite data is also crucial for time-critical applications in agriculture. With an increased demand for satellite data that is used in agricultural applications, the need for near real time information would only grow further. Remote Sensing based crop yield prediction, pre-harvest production estimation and crop damage assessment are all time-sensitive and would require data to be available at critical periods of the crop cycle.
Under normal circumstances, the remote sensing user community could only access ACRES satellite data that was a few days old even for emergencies. It took a day or two for raw data to be transferred from the acquisition sites to the processing facility and an additional 2 to 5 days to generate a product through standard processing. For a useful near real time service, the shipping of raw data from the acquisition facilities to the processing facility had to be replaced with on-line transmission of data from the acquisition sites.
On account of the complex nature of satellite data sets and large data volumes involved, the key design objective for a near real time service was to reduce drastically the time it took for raw data from Alice Springs and Hobart to reach the processing facility in Canberra through a high-bandwidth communication link. Once processed, the data had to be made available in a form that enabled fast and efficient on-line delivery through the File Transfer Protocol (FTP) for users to access. The STAR service had to be designed to provide near real time data from the major satellites supported by ACRES - Landsat 7, SPOT, RADARSAT and ERS.
A STAR is born
The ACRES Speedy Transmission After Reception (STAR) service was primarily driven by users’ need for speedy access to satellite data. The STAR project used the advances in communication technology (ie increased bandwidth) to achieve reduction in data transfer time from the data acquisition facilities to the Data Processing Facility (DPF) and image compression techniques to achieve reduction in data volume. The STAR service was enabled primarily through the installation of a high-speed communication link between the data acquisition sites at Alice Springs & Hobart and the DPF in Canberra.
The high-speed communication link is based on frame relay technology with a bandwidth of 1024 kilo bits per second (kbps) and a Committed Information Rate (CIR) of 256 kbps from Alice Springs. The capacity of the link from Hobart is 512 kbps with a CIR of 128 kbps, the link capacities are scalable if required. New hardware was acquired and installed at the acquisition facilities and software modifications were done at both acquisition facilities and the DPF to support and implement the project. Once installed, the link was tested for its performance in transmitting different data sets and data volumes with trials conducted through ACRES distributors.
Image compression techniques available through off-the-shelf software packages were used to reduce data volumes for FTP transmission. The formats and compression techniques that are available through the STAR service are shown in Table 1. Out of a number of bands available for different data sets, an intelligent selection of bands to provide information that is specific to a particular application also helped reduce data volume for FTP transmission. Simultaneously, the complete data set was also generated on conventional media. This enabled quick access to the most important information via FTP and the complete data set on conventional media could be sent through courier.
ACRES STAR service parameters
The ACRES STAR service provides users with access to digital satellite imagery products within 12 hours of a satellite overpass. The service features priority acquisitions by ACRES ground stations, immediate transmission of raw data to the Canberra processing facility via a new high-speed communication link and high priority processing to user specifications. The STAR service enables users to place requests for a satellite to be programmed for data acquisition over their particular area of interest and have the data delivered on-line by FTP.
Figure 1 Schematic diagram showing acquisition and delivery of NRT satellite data through the STAR service
ACRES have a network of distributors who promote the distribution of ACRES products and services to end-users. Users can contact an ACRES distributor for information on earliest available acquisition dates for the different satellites to cover particular areas of interest. A schematic diagram showing the acquisition and delivery of satellite data through the STAR service is given in Figure 1. The key service parameters of the STAR are given in Table 1. ACRES also offers priority processing of orders with a turnaround time of 36 hours (from the time an order is confirmed to when the data is ready for dispatch). Users would pay $200 in addition to the normal product price when using this service.
Table 1 Key service parameters of STAR
Landsat 7, SPOT, RADARSAT and ERS
Delivery and turnaround time
Within 12 hours of acquisition, the User will be notified that the processed product (full resolution and/or sub-sampled) is available from the ACRES FTP site. (It is possible that this turnaround time will be significantly less than 12 hours.) In addition, the full resolution product will be written to media in the same time frame and sent by the next available courier.
Data formats and media
Full resolution digital image is available in ACRES standard formats and on ACRES standard media.
Compressed image formats are available in JPEG (1 or 3 bands), GeoTIFF (1 or 3 bands), MrSID (1 or 3 bands) or Enhanced Compressed Wavelet (multiple bands).
A successful acquisition occurs when ACRES downloads the required data from the satellite. For Landsat 7 and SPOT, a successful acquisition also means that the product area ordered by the user is obscured by a total of < 10% cloud cover, or any greater percentage defined by the user at the time of ordering.
$400 in addition to the standard ACRES price for that product.
Major benefits of ACRES STAR service
The STAR service can provide vital and timely satellite image data for emergencies like bushfires, floods or oil spills and help in containing damage and managing relief operations. Through the STAR service, agencies responsible for protection of our environment have quick and easy access to information in near real time that can help them in relief operations during environmental mishaps or natural disasters. The farming community will benefit through the STAR service by having access to satellite imagery for time-critical events in the crop calendar. Image data at critical times during the crop cycle can help estimate crop yields much before they are harvested or provide indications about crop vigour or damage. Routine use of the service to obtain more up-to-date yield estimates and crop health indicators can provide farmers with an important edge in the market place. ACRES also plans to use the technology that underpins the STAR service to provide other services like on-line subscription of data from sensors with low resolution and high repeat cycles such as MODIS and AVHRR. Data available through the subscription service would benefit agricultural applications like management of drought, which would require regular monitoring on a regional level.
ACRES STAR service case studies
Bushfire monitoring using ETM+ data
Within a few hours of its launch, the STAR service was used to provide satellite imagery covering a bushfire that threatened a vital communications installation outside Perth. The Landsat 7 ETM+ image of Perth shown in Figure 2 was acquired on 15 February 2001 at 12:55 hrs EST by the Alice Springs ground station. This data set of 900MB was transferred in 4 hours to Canberra for processing. A standard path oriented image was generated and compressed to an ECW file for electronic delivery to Department of Land Administration (DOLA) at Perth by 18:00 hrs. In less than 5 minutes, 60MB of compressed data was downloaded and ingested into their systems for further analyses. DOLA was delighted with the new service and the quality of the compressed product.
Figure 2 Landsat ETM+ image over Perth
DOLA’s client, Fire and Emergency Services (FESA) WA are excited at the prospect of receiving imagery so quickly. They would be using this scenario to push for greater use of satellite imagery during bushfires.
Agricultural application using ETM+ data
A Landsat 7 ETM+ image of Emerald town (west of Rockhampton) acquired on 25 January 2001 at Alice Springs was transferred in 3 hours to Canberra for processing. It was processed within 2 hours and delivered electronically to AGRECON Pty Ltd via FTP. It took them 22 minutes to download the 70 MB ECW compressed image of 6 bands. “This trial was more than successful. We really were impressed with receiving the imagery 5 hours after acquisition” reported AGRECON. They believe that ACRES STAR service has a great potential for crop monitoring studies.
Flood mapping application using SPOT 4 data
The SPOT 4 Xi image of the Queensland floods shown in Figure 3 was acquired at 11:20 EST on 12 February 2001 at Alice Springs. It took only 30 minutes to transfer the data from Alice Springs to the processing centre in Canberra. ACRES processed this data set and a JPEG compressed image was ready for download from AUSLIG’s FTP server by 13:50 hrs, about 2 hours and 30 minutes after acquisition. Analysts at Geo Mapping Technologies downloaded this image in 15 minutes using a 56K-modem and dial-up Internet connection.
Figure 3 SPOT 4 Xi image over Barwon River
Despite the high compression ratio of the JPEG image (1:22), Geo Mapping Technologies reported that it is of good quality and highly suitable for flood mapping.
This image is almost cloud free and shows extensive flood plains of the Barwon River, which are partially flooded at the time of acquisition. Geo Mapping Technologies reported that “the trial was successful and exceeded the specification of the proposed STAR service in that the image was delivered in less than 3 hours of acquisition”. This case study also demonstrated that highly compressed JPEG images could be used for identification and mapping of flooded areas and readily transferred via standard modems without the need for an expensive ISDN link.
Surveillance of fishing vessels using RADARSAT data
A RADARSAT standard beam (S6) image covering an area southwest of Stewart Island, New Zealand was used for this study. ACRES managed to get the acquisition granted within 48 hours before the satellite pass. The image was acquired early morning at 04:30hrs EST on 6 February at Tasmanian Earth Resources Satellite Station (TERSS), Hobart and was transferred to Canberra within 6 hours of acquisition. It was processed and ready for download from AUSLIG’s FTP server by 14:00 hrs the same day, about 9 hours 30 minutes after the acquisition. Landcare Research at New Zealand, who participated in this study, downloaded the full resolution product within 1 hour and 30 minutes, analysed the data and sent the results to their client by the same evening (6 February 2001). Their client was impressed with the new service.
Online satellite imagery - bought on the spot
ACRES offers an off-the-shelf satellite image product that is available through the Internet – GEODATA SPOT-LITE. It can be downloaded at any time from AUSLIG’s web site at www.auslig.gov.au and used directly in a GIS environment. Userss can download SPOT-LITE even when they are in the field - a computer and access to the Internet are the only requirements.
GEODATA SPOT-LITE is a satellite image mosaic covering most of Australia that can be purchased and downloaded directly off the Web. It is available in a series of "tiles" each covering an area of approximately 25km by 25km. SPOT-LITE is derived from data acquired by the panchromatic (PAN) sensor on board the SPOT series of satellites. SPOT-LITE was created as a result of AUSLIG’s use of PAN imagery from SPOT for revision of its 1:250 000-scale topographic maps. SPOT-LITE tiles are supplied in industry standard GeoTIFF format. This means SPOT-LITE can be displayed easily by any graphics package that can read the TIFF format. In addition, many Geographic Information Systems (GIS) and image analysis systems can read the geo-referencing information stored in the GeoTIFF header and readily integrate SPOT-LITE tiles with other geo-referenced information.
New Features of SPOT-LITE
In response to user suggestions, new features have been added to the SPOT-LITE system. Variable sized sub-tiles can now be purchased - the minimum size of the sub-tile is 10 km x 10 km at a price of $50. The sub-tile window can be stretched and positioned anywhere within a full-tile (25 km x 25 km). This major change makes SPOT-LITE affordable to a wider range of users.
The catalogue search has been improved for a faster start-up and less memory is consumed on the user's computer. Sample SPOT-LITE tiles are now available as free downloads.
Table 2 Product specifications for SPOT-LITE
SPOT PAN (Panchromatic) imagery
10 metres for near vertical viewing angles
Date of Acquisition
Single date for each tile with age ranging from six months to five years old (90% of tiles in this database fall within this specification). The exact date is indicated in the SPOT-LITE metadata.
Geocentric Datum of Australia (GDA94), or Australian Geodetic Datum (AGD66).
Universal Transverse Mercator (UTM), or Plate Careé (a form of Equirectangular);
15' latitude by 15' longitude for Equirectangular projection - no overlap between adjacent tiles; UTM tile sizes vary but are always slightly larger than 15' by 15' - there is a small amount of overlap between adjacent tiles. Within a tile, rectangular sub-tiles of any size up to a maximum of 555 sq km can be chosen. Minimum size of a sub-tile is approximately 6' latitude by 6' longitude (10 km x 10 km).
.0001° by .0001° for Equi-rectangular projection; 10m by 10m for UTM projection.
Average error 20m (not worse than 60m).
All tiles have had a linear contrast stretch and edge enhancement applied
GeoTIFF, JPEG compressed to quality factor 50.
Uncompressed GeoTIFF files are about 6.25 Mb per tile. When compressed for download files sizes vary between 0.26 and 1.5 Mb per tile with a typical average size of 0.87 Mb
Cloud cover is less than 10 % per tile. However, there are a few tiles that have more than 10% cloud cover because of the difficulty in getting cloud-free imagery in those areas.
Recommended Retail Price is $300.00 (GST included) per full tile. The minimum price of a sub-tile (10 x 10 km) is $50 (GST included) and any extra pixels on top of this minimum are charged at a rate of $0.55/sq km.
Improvements have been made at the browse level enabling half-tile scrolling which is useful for selecting multiple sub-tiles from adjacent tiles. Searches for SPOT-LITE tiles can now be performed by specifying the 100K or 50K map number. Table 2 provides details about the product specifications for SPOT-LITE.
How SPOT-LITE can be used
SPOT-LITE can be used for a multitude of purposes. SPOT-LITE can be used in "stand alone" mode as a substitute for a map, it is more up-to-date and contains more detail than many maps. SPOT-LITE can be used as a background for other geographic information datasets such as roads, railways and towns, it adds in the extra detail such as vegetation, land use and minor tracks. SPOT-LITE can be used to update geographic data bases for example, new roads, towns, powerlines and changes to vegetation are all clearly visible on SPOT-LITE. It can be linked with navigation systems such as GPS making it much easier to see where you are on the ground. A SPOT-LITE sample over an agricultural area is shown in Figure 4.
Figure 4 SPOT-LITE over an agricultural area
Farmers can use SPOT-LITE in their farm management plans, local government authorities could use it for land-use planning, emergency services could use it for hazard identification, map updating and in their emergency response systems.
SPOT-LITE being an off-the-shelf product offers no choice with respect to the time of image acquisition. SPOT-LITE is ideal for GIS applications that need the extra spatial detail available from satellite imagery and not constrained by currency of the image. The low price and ease with which SPOT-LITE can be downloaded off the web at any time satellite imagery is required, is a big advantage to users.
How to purchase SPOT-LITE
A simple to use graphical catalogue system on AUSLIG’s web site www.auslig.gov.au acts as the interface for purchasing SPOT-LITE. The opening page of the catalogue displays a map of Australia, overlaid by a grid depicting SPOT-LITE images that are currently available. Progressive zooming and selection displays the SPOT-LITE tile for the area of interest along with the metadata for the tile. Users have the choice of purchasing entire tile(s) or a part of the tile(s).
When the user makes a selection, the user interface dynamically displays the price of the selection (tile or sub-tile). The selection is then downloaded for use. SPOT-LITE data comes in a compressed and encrypted form for efficient and secure online delivery. Users are prompted to select a distributor of their choice from a drop-down list in order to organise payment arrangements in exchange for the decryption key, which enables the use of the encrypted tile(s). Decryption of the downloaded tile(s) is enabled by a module called the ‘Unlock Tool’, which resides on the users’ computer through a one time installation of the module from the SPOT-LITE web page.
The author wishes to thank Shanti Reddy at ACRES for sharing the results of STAR service case studies that were undertaken.