New dimension in Earth observation

Among many applications, ride-sharing taxies guided by real-time geo-locations have empowered common people to enjoy the utility of Earth observation from the sky in their daily lives.

A seminar in SoftExpo 2019 introduced a possibility of Earth observation through the fusion of images captured by satellites, manned and unmanned aerial vehicles (UAVs).

This fusion approach expands the possibility of remote sensing from understanding the situation to taking action on the ground, whether for precisely distributing fertilisers or estimating river erosion or assessing road damage in centimetre accuracy.   

Over the last 70 years, the era of space-born observation platforms (satellite), fitted with diverse sensors starting from camera to synthetic aperture radar, has come a long way to unlocking the possibilities of remote sensing.

In addition to defence purposes, commercial applications are increasingly benefitting from images sent by orbiting sensing platforms.

Despite progress in the frequency of traversing area of interest and resolution of images, satellite-born remote sensing are facing limitations.

But fortunately, we are witnessing the increasing complementary roles being played by both manned and unmanned aerial imaging platforms.

The fusion of these three platforms is taking Earth observations at higher height.

As of April 2018, there were 1980 operational satellites, according to the Union of Concerned Scientists (UCS) satellite database.

Among them, Earth Observation (EO) satellites (684) currently account for over one-third of them.

Due to increasing innovations in using images and data sent by these satellites, the number of EO satellites has been rapidly increasing, reaching 684 in 2018 from 192 in 2014.

More than 80 percent of EO satellites have onboard optical, radar, infrared, and hyper-spectral/multispectral imaging sensors.

Government agencies, civilian applications and military are the major users of imaging and data products of the EO satellites.

At the beginning, governments, primarily for the purpose of military, used to dominate satellite launches.

But in the recent past, there has been increasing launches from private companies for the purpose of trading images and data products.

Increasingly, government agencies, including military, are becoming customers of imagery products delivered by commercial satellite operators.

The usage of satellite imageries in major civilian projects has already started in Bangladesh.

For example, a local IT firm did a 3D mapping from very high resolution (0.5 metres) satellite images and also prepared a digital elevation model of 10-metre resolution of Dhaka Metropolitan Development Plan area for Rajuk.

Similarly, the preparation of a development plan for Benapole-Jessore Highway Corridor Project benefitted from 3D mapping from satellite images.

Dhaka WASA also outsourced work for developing maps from 3D satellite images for the design and implementation of water supply projects.

Satellite imagery usages also generate service revenue for local IT firms. Roughly, the derivation of insights from $1 worth of image produces $2 to $3 data analytic and mapping service revenue.  

Satellite imagery plays an important role in offering timely, reliable and accurate maritime security and environmental monitoring services, which will come to use in exploiting the blue economy potential.

The fusion of satellite images produced by radar and optical sensors with images produced by manned aerial vehicles could lead to all-weather detection, classification and tracking of illegal or unauthorised vessels in exclusive economic zones, territorial waters and restricted areas.

Satellite imagery can be used to detect and classify infrastructure whether for planning, compliance or development. Satellite images are now extensively used in mapping, 3D modelling, detecting change over time, asset and facility monitoring, and humanitarian and disaster response.

Most EO satellites carrying remote sensing instruments are orbiting the Earth at relatively low altitudes; below 500-600 kilometres is in generally avoided, because of the significant air-drag.

By lowering the altitude and adopting higher resolution sensors along with optics, resolution of images provided by EO satellites has increased significantly over the decades, reaching 30 cm.

Further enhancement of resolution is not a viable option, due to the economics of cost of image products per square km and the cost of launching and operation.

As most of EO satellites use the sun for radiating energy from the Earth, these satellites become non-functional during night time. Moreover, cloud and fog also limit the quality of images produced by the satellites.

Although radar sensors can address these limitations, often images delivered by them do not provide the same type of information. Rather, radar complements other passive sensors relying on electromagnetic energy radiated and reflected by Earth.

Images of EO satellites provide high-level intelligence of large areas. For example, river erosion or overall road damage could be detected in satellite images, but getting further clarity leading to accurate estimation could be provided by UAV or drone-based imaging platforms.

Although drones are perceived as toys, modern UAVs could be fitted with diverse, powerful sensors, starting from a low-cost video camera to LIDAR to multispectral as well as infrared image sensors, making them high-performing remote sensing platforms.

High-resolution images produced by UAVs could be processed in developing both 2D and 3D models of the landscape in developing high-resolution maps.

Among other applications, through data analytics, intelligence could be extracted from images captured by UAVs to develop fertility and moisture maps of lands, and also chlorophyll maps leading to precise fertiliser dose determination.

With very high accuracy, river erosion could be assessed, and the estimation of road repairing cost could be determined from UAV images.

3D models developed from images of a construction site could be compared with the planned model to understand the progress as well as compliance.

Moreover, UAVs fitted with gas and infrared sensors could produce images with signatures of the health situation of gas pipelines and power networks.

Across the globe, UAV imaging-based remote sensing service innovation has been growing rapidly.

In the estimated $127 billion of global UAV-based remote sensing industry, the UAV analytics market is projected to grow from $1.57 billion in 2017 to $5.41 billion by 2022, at a CAGR of 28.11 percent from 2017 to 2022.

Which remote-sensing platform is more suitable than others in a particular task is a question.  The common solution is to choose a satellite when a “macro” view of the terrain is needed. UAVs are great to get the “micro” view of fields of specific areas of interest, often detected from the satellite-provided “macro” view.

Basically, it all depends on the goals of the end user and what they want to accomplish.

Moreover, satellite imagery also provides the basis for planning the mission of UAVs.

Satellite imaging is often economically more attractive than other means when a large amount of data over a vast area must be gathered quickly.

Aerial imaging complements satellite's capability, consequentially expanding the possibility of remote sensing.

It is being reported that some companies are already trying to merge their fleets of satellites with drone data to provide their clients with a holistic approach tailored to their needs.

Often UAVs are perceived as toys creating nuisance in the airspace. Such perception often leads to the restricted regulatory framework.

But such regulatory approach appears to be a barrier to the exploitation of UAVs as a remote sensing platform.

On the other hand, the emergence of a considerable number of commercial satellites fitted with diverse sensors is opening the opportunity of fusing satellite imagery with images captured by manned and/or unmanned aerial vehicles to derive actionable insights in serving diverse purposes.

The writer is a professor of North South University's department of electrical and computing engineering.