SATELLITE IMAGERY TECHNOLOGY: THEN AND NOW

Steve Critchlow, Group Managing Director, Critchlow Geospatial

There is perhaps no better example (or visual comparison) of the evolution of spatial technology than satellite imagery technology – and the importance of this technology has never been more critical than today. The image below was taken on Tuesday, February 21 in Puketapu, Hawke’s Bay, a week after Cyclone Gabrielle hit.

As the country navigates its way through this latest natural disaster, knowing that authorities today can rely on the availability of such highly detailed data shows just how far we’ve come.

But let’s go way back to the beginning when the NASA weather satellite TIROS-1 sent the first picture of Earth from space on April 1, 1960. It was obviously both revolutionary and revelatory to view imagery of this kind for the very first time.

Satellite imagery and associated technology, of course, has advanced significantly since the launch of Landsat 1 in the 1970s (perhaps not as quickly as many geospatial experts would like).

In truth, until pretty recently, satellite imagery technology had been a source of great frustration – so much potential, but it was clear that potential wouldn’t be realised fully until next generation optics (and supporting technology) came on stream.

Adding to this frustration was the knowledge that if you didn’t have serious in-house expertise, as well as the required (and expensive) hardware/software, then any real-world business applications were largely out of reach for most organisations.

Quite simply, these limitations meant that for many years, satellite imagery technology just wasn’t ready for mainstream use and subsequently was never adopted at the scale that its initial promise suggested it would be.

Today, it’s a different story.

Quietly and somewhat behind the scenes, over the past few years, satellite imagery technology has properly come of age.

Back then, of course, the images were constructed by stitching together thousands of individual photographs; and it was really only possible to discern land and water boundaries, or large scale cloud formations.

The next big technology leap occurred on July 23, 1972, when the Landsat 1 satellite was launched. That’s really where modern ‘earth observation’ satellite imagery technology (as we know it) started.

The impact on cartography and the geospatial sciences of Landsat 1 data cannot be overstated: it was immediate and fundamental; country boundaries were redrawn and new islands discovered.

Within days of the launch, Landsat 1 captured imagery of an enormous fire burning in central Alaska, allowing scientists to see, for the first time, the extent of fire damage via satellite while it was still burning.

Landsat 1 was in service for over six years and, during that time, obtained images that covered nearly 75% of Earth’s surface.

Equipped with cameras and instruments operating in both the visible and near infra-red spectral bands, Landsat 1 was capable of up to 80-metre ground resolution.

The first advances in enhancing the data with computer technology and software were also pioneered during this time, allowing some of the spectral band data to be digitally processed and improved.

Today, providers can routinely offer native 30cm resolution and derived resolution high-definition imagery (via algorithms) of 15cm.

In addition, the recent advances in optics, remote sensing, artificial intelligence, machine learning and cloud computing now mean satellite imagery is more powerful and accessible than ever before and is driving newer and ever more granular applications.

This complementary technology is further enabling the use of multispectral and hyperspectral capabilities allowing users to more quickly and easily visualise and monitor change, as well as determine and distinguish between material features on the surface of Earth.

Multispectral and hyperspectral satellite imagery

Multispectral imaging works by capturing image data within specific wavelength ranges from across the electromagnetic spectrum. This can include frequencies such as infrared and ultra-violet – these are wavelengths beyond the visible light range for humans and allow for the extraction of information that the human eye would be unable to capture.

With multispectral satellite imagery, it is possible to differentiate materials by what is known as their ‘spectral reflectance signatures’. These unique ‘fingerprints’ enable identification of materials, for example, the spectral signature for oil can help detect and ascertain the area of oil spills at sea.

Hyperspectral imagery is next level again and enables segmentation and classification of land and aquatic features to a very granular level (but of course, like anything to do with satellite imagery – also at scale).

For example, hyperspectral imagery can identify and quantify molecular absorption, inferring biological and chemical processes, and has been used in this capacity to monitor the application of pesticides for quality control and optimum dose coverage.

Commercially available synthetic aperture radar imagery

When you combine all these advances in detection, processing power and accessibility with the capability for new imagery to be captured daily, you have an incredibly powerful tool for understanding and anticipating change (both human created and natural).

This kind of easy access and on-demand intelligence is ideal for assessing risk, monitoring land use, and planning infrastructure and development.

The applications for environmental protection and emergency response are also huge, particularly when you consider the ability of SAR imagery to penetrate both smoke and cloud cover.

Then and now

With over 20 years’ worth of vast imagery archives now readily accessible, satellite imagery provides unique historical context around change to our planet via what is essentially a ‘then and now’ digital time machine.

These archives also plainly highlight the difference between satellite imagery technology in its infancy and what it is capable of today. As is often the way in geospatial, the difference between then and now is most powerfully demonstrated visually.

Below is the first image of Earth from space taken by TIROS-1 on April 1, 1960. Compare that with the Capella image.

Clearly, the difference in resolution between the very first satellite images of the 1960s and the latest satellite imagery is obvious and striking. However, even this doesn’t fully

One of the most significant advances in satellite imagery technology recently is the commercial availability of synthetic aperture radar (SAR). This technology uses radar to capture images of Earth’s surface, and depending on the use case, its capabilities are far more powerful than optical satellite imagery. This includes enhanced change detection capabilities and SAR’s ability to penetrate cloud, smoke and darkness.

Accessibility and currency

Cloud computing and flexible new business models around the data licences for software and data make it easier and more cost-effective than ever to access satellite imagery in a timely and automated manner.