What is “remote sensing” and how well do we understand this term? How does it work and why do we need remote sensing? As stated in many text books and other publications the term remote sensing is commonly used to describe the science—and technology—of identifying, observing, and measuring an object without coming into direct contact with it. Based on this definition, the first ‘remote sensing’ was undertaken by Gaspard-Félix Tournachon, who produced the first successful aerial photograph of a French village using a hot air balloon in 1858.
In his introduction, Graham Ezzy emphasized that the talk was an overview of remote sensing, as the field is vast and crosses into many areas of science and technology with many challenges and risks including political. Aircraft—including Unmanned Aircraft Systems (UAS) or drones—and satellites are the common platforms for remote sensing of the earth and its natural resources. UAS are not new: the use of unmanned flight pre-dates human-piloted flight. Aerial bombardment of Venice in 1849 was undertaken (albeit ineffectively) by unmanned hot-air balloons, and similar balloons were used in the American Civil War.
Conventional land-based observations are typically collected at fixed intervals with limited spatial coverage, whereas satellite remote sensing (SRS) allows for continual monitoring on the global scale. Since the launch of TIROS-1 on 1 April 1960, a large number of ‘sensors on-board’ satellites, with improved temporal, spectral, and spatial resolution, have been employed to gather data and information regarding the Earth’s atmosphere and surface (land and ocean). These ever improving technologies associated with new image processing techniques allow users to generate a variety of different types of information from satellite data. As with any sensor, Graham stressed that they needed to be calibrated and validated.
View from Ikonis satellite
Reinforced with examples of past, present and future sensors, the talk presented a wide range of applications and techniques in many fields of remote sensing including:
- Landsat—its incredible, long-lived legacy has archived Earth’s history since 1972
- Remote sensing of the environment and the role of satellite remote sensing in climate change studies
- Hazard assessment— to track tropical cyclones, earthquakes, erosion, and flooding. Data can be used to assess the impacts of a natural disaster and create preparedness strategies to be used before and after a hazardous event.
- Natural resource management— to monitor land use, map wetlands, and chart wildlife habitats. Data can be used to minimize the damage that urban growth has on the environment and help decide how to best protect natural resources.
- Extracting mineral deposits with hyperspectral remote sensing
- Predicting retail earnings and market share by counting cars in parking lots.
Several satellites currently monitor carbon dioxide emissions, including Japan’s GOSAT, the United States’ Orbiting Carbon Observatory-2 (OCO-2), and China’s TanSat. OCO’s measurements are designed to be accurate enough to show for the first time the geographic distribution of carbon dioxide sources and sinks on a regional scale. The proposed Sentinel satellites would precisely measure greenhouse gases around the world. However, the proposed SCARBO constellation of 24 satellites working together (they weigh just 50 kilograms each, roughly one-tenth the mass of OCO-2 or TanSat) would be able to cover the globe once a week, but could fly over particular areas of interest once a day. Together they could monitor frequent changes in carbon emissions, such as morning and afternoon surges from an industrial area.
However, satellite data often contain uncertainties caused by biases in sensors and retrieval algorithms, as well as inconsistencies between continuing satellite missions with the same sensors. In particular, there are concerns about the suitability of satellite data for monitoring and understanding climate change. Climate change studies require observations to be calibrated/validated and consistent, and to provide adequate temporal and spatial sampling over a long period of time.
Remote sensing is now a vital element in humanity’s ability to monitor the health and state of the Earth and optimistically will ultimately become an element when the collective decision is made to look after it properly.