sar imagery provider

Choosing the right SAR imagery provider is all about their quoted revisit frequency. Or is it?

So you have an application or use case that lends itself to the use of SAR satellite imagery, for example flood monitoring, disaster response, illegal fishing, land and asset motion etc. You already know that the resolution and/or revisit frequency of open source SAR imagery from the likes of Sentinel-1, PALSAR, RADARSAT-1 etc. won’t meet your needs so it is time to review the offering of the growing number of providers of commercial SAR imagery.

Aspects such as price, imagery resolution and imagery footprint are easy to flush out, but if your use case requires a provider who can provide imagery fast, when and where in the world you need it…..then more caution and questioning will be required to understand what a provider’s true revisit frequency really is.

The reasons why true and quoted revisit frequencies differ

Here are the main reasons why the true revisit frequency is always lower than the very impressive quoted revisit frequency numbers bandied around by imagery providers…..

Ground Track Repeat imagery

If your use case requires, or is best served by the use of coherent Ground Track Repeat imagery then the usable revisit frequency can easily drop from many times per day to once per day or even less. That is because Ground Track Repeat imagery is imagery taken of the same area, with the same look angle and direction. When providers quote revisit frequencies they are talking about how many times per day, on average, one of their satellites can image the same point on the earth unconstrained by look angle or direction. No surprise then that the usable and quoted revisit frequencies are very different numbers. You shouldn’t have too much trouble getting this info out of a provider.

The payload duty cycle

The next killer is a SAR satellite’s payload duty cycle in mins per orbit. Typical commercial SAR satellites take about 90 mins to orbit the earth once and have duty cycles that range from just a couple of minutes up to 10 plus minutes per orbit. Why? Satellites are solar powered so while SAR satellites can capture imagery day and night they can only recharge when they are on the sunny side. Also SAR sensors, which are active sensors sending out and receiving radar waves, require much more energy than optical image sensors, which are passive sensors. These two facts mean that a satellite passing over your target area may actually be recharging and unable to capture your image. Some providers are very open about this, others much more cagey. Rule of thumb here is that the bigger the satellites are, the bigger the onboard solar panels and power storage will be, giving a higher payload duty cycle and more minutes of imagery action.

Next comes customer priority

Imagine two clients have requested different imagery captures that can only be fulfilled by the same satellite sensor, assuming power is not the constraint, there might not be enough time between capturing one image to move the sensor into the correct position to capture the second image. Different providers handle this in different ways, premium tasking payments, customer ranking based on purchase volume, promises not to change an image capture request once confirmed etc. Either way a few questions about the free capacity they have over your geographical area of interest, and how they handle capacity constraints will flush out where you might stand in the customer pecking order.

Last of all, mistakes do happen

Satellites are extremely reliable pieces of equipment built and tested to withstand the unfriendly conditions of space but now and again a captured image may not pass the required quality checks. Again some providers will be more transparent about how often this happens than others, so all the more reason to ask the question.

There are a few other subtleties relating to latitude, data storage and downlink duty cycles but covering the 4 points above will give you an accurate overview of what true and usable revisit frequency can be delivered by any SAR imagery provider.

Should you still be excited about SAR imagery? Oh yes….

So while the true and usable revisit frequency will actually be well below a providers quoted revisit frequency that isn’t to say that there isn’t an exciting, very real, and exponentially increasing SAR imagery capture capacity being provided by a growing group of innovative providers. There really is. Just that a little care, expertise, and a few extra questions are required to pick the right imagery provider for your use case.

I would love to hear your views and experience on the mysteries of SAR revisit frequencies and how that has impacted your choice of provider.

At Spottitt we provide our clients with the broadest range of automated satellite derived asset monitoring services on the market, all at attractive pricing. Our expertise includes the integration of both open source and commercial data from optical, SAR, GHG and other satellite sensors.

Feel free to get in touch.

Lucy Kennedy

Lucy Kennedy

Spottitt CEO and FIRE EO Evangelist for Infrastructure

Our latest news:

Spottitt Provides a Solution to Automatically Detect Changing Conditions on the NSW Road & Rail Network

Spottitt became Finalist in Transgrid’s Challenge for real-time insights for company’s easement route planning and Champion for Transport for NSW Challenge for tracking safety of roads and railways using satellite data.

The New South Wales network includes 6,800 route kilometres of operational rail lines and 17,600 km of state roads and highways.

TfNSW has identified Earth Observation satellites as a valuable addition to the monitoring technologies currently deployed and was looking for innovation to automatically detect changing conditions of network and potential risk modelling.

Satellites Drones Geospatial Data Collection Comparative Analysis

Deciding Between Satellites and Drones for Geospatial Data Collection: A Comparative Analysis

In recent times, the landscape of asset monitoring has witnessed a transformative shift with the emergence of advanced technologies, particularly satellite and drone systems.

The utilization of Earth observation satellites for monitoring purposes began gaining momentum in the late 20th century. Free government programs, such as those initiated by NASA and the European Space Agency (ESA), played a pivotal role in providing open access to satellite imagery. These programs not only facilitated scientific research but also allowed industries to leverage satellite data for monitoring critical infrastructure and environmental changes.

spottitt transgrid transport deloitte

Spottitt to Collaborate with Transgrid and Transport for NSW

Spottitt has been selected by Transport for NSW and Transgrid to apply satellite-based and AI-powered technology to automatically detect changing conditions in the NSW road and rail network and to provide real-time insights for Transgrid’s easement route maintenance and planning, respectively.

These projects will be conducted within the GRAVITY Challenge 06 program led by Deloitte Australia, an initiative that brings together start-ups, scale-ups, entrepreneurs and universities to address real industrial and environmental problems using space data. The Collaborate Phase will continue until mid-March 2024.

climate change EU UK Ireland satellite data

Weathering the Storm: Climate Change Threats to Power Grid Infrastructure

As our global climate continues to undergo profound transformations, the challenges posed by climate change are increasingly felt across various sectors of society, including critical infrastructure.

Climate change, characterized by rising temperatures, increased occurrences of extreme weather events, and shifting precipitation patterns, have exposed vulnerabilities within power networks. Often designed under the assumptions of historical climate patterns, now they are increasingly susceptible to the new normal of extreme weather, prolonged heat waves, and more severe freezing.

InSAR analysis Infrastructure Monitoring Sentinel Imagery

InSAR Analysis and Corner Reflector Experiments for Infrastructure Stability Monitoring Using Sentinel-1 Imagery

National Grid Energy Transmissions (NGET), which owns and maintains the high-voltage electricity transmission network in England and Wales, conducts invasive analysis annually to monitor the towers most at risk of movement. Moreover, the NGET inspection teams perform annual line walking activities and monthly substation inspections during which they visually assess the presence of asset motion. These interventions are crucial to avoid issues which may cause expensive assets replacements or reconstruction. It costs NGET over £6 million per year to monitor only 1% of their most at risk assets.


Utilizing Satellite Data to Mitigate Pipeline Failures and Risks

The operation of oil and gas transmission pipelines entails inherent risks associated with the potential for unintentional product releases. Oil and gas product releases have traditionally been treated as safety issues due to the risk of explosions and asphyxiation, but increasingly, the environmental impact of unintentional product releases is fast becoming the key risk to be reduced and avoided via Leak Detection and Repair (LDAR) programs.