With the launch of the ZACube-2 nanosatellite, a new technique of wildfire detection and monitoring from space will be evaluated. Potassium is an essential plant macronutrient and all vegetation biomass fires exhibit characteristic spectral “K-line” emissions in the near infrared (NIR), which can be isolated and observed with suitable optical filtering. However, as a new technique, the effectiveness of this kind of sensor from a space platform is unknown. The magnitude of the K-line emission signal seen from space is contingent on many factors, including the concentration of potassium in the biomass fuel, fire size and intensity as well as atmospheric state. The architecture and preparation of the flight model K-line sensor hardware is described, together with the approach to verification and validation of the sensor characteristics and performance on-orbit.
Satellite remote sensing of inland water bodies has great potential for ensuring water quality and for obtaining reliable data which can be used for decision making. This is a rapidly evolving technology that is now widely utilized throughout the globe for providing a broad as well as detailed perspective on earth-system status and change. Inland water processes, such as eutrophication, may have a major impact on human life and can lead to environmental disasters. This study investigates the optical effect of atmospheric aerosols on remote sensing of the water-leaving radiance (Lw) at Roodeplaat dam. An in-situ measurement field campaign was performed at Roodeplaat dam (Pretoria) during the 2016 winter season, in relation to calibration and validation of Sentinel 2 and Sentinel 3 satellite data. In-situ measurements were performed simultaneously with the satellite overpasses at the dam. In-situ measurements included Aerosol Optical Thickness (AOT), water vapor column and downwelling spectral irradiance as well as the remote sensing spectral reflectance of the dam, Rrs. A radiative transfer code (Modtran) was used to predict the radiance at the Top of Atmosphere (TOA), compared to actual measurements from Sentinel 2 and 3. Sensitivity analysis demonstrated that retrieval of water-leaving radiance at small water bodies such as Roodeplaat dam was sensitive to aerosol optical properties as well as total column.
KEYWORDS: Modulation transfer functions, Imaging systems, Satellites, Commercial off the shelf technology, Refractive index, Sensors, Thermal modeling, Cameras, Temperature metrology
The paper presents a laboratory methodology for determining the space environmental effect on the focus of an objective lens for an earth imaging payload on a small satellite. Components used in space applications should undergo rigorous screening and testing, including thermal-vacuum (TVac) testing. These tests reduce risk and can provide critical information leading to risk mitigation strategies contributing to mission success. The global value and market for CubeSats for both commercial and scientific applications is fast growing and this has led to the demand for environmental test equipment. Existing facilities around the globe for satellite TVac testing are typically expensive and difficult to access and also oversized for nanosat applications. As a result, CSIR Optronic Sensor Systems embarked on developing a laboratory test procedure and a small scale TVac chamber based on commercial off-the-shelf (COTS) components. The specific purpose was to quantify the defocus of a COTS imaging lens under vacuum and over a specific operating temperature range. The TVac defocus is caused by variation of the refractive index of air with pressure and variation of the refractive index of glass with temperature. Temperature-related dimensional changes also contribute. The tests provided repeatable measurements leading to a TVac model for the defocus behaviour of the lens. The model allows for setting of a compensatory or “preemptive” defocus before launch.
Wildland fires are a widespread, seasonal and largely man-made hazard which have a broad range of negative effects. These wildfires cause not only the destruction of homes, infrastructure, cultivated forests and natural habitats but also contribute to climate change through greenhouse gas emissions and aerosol particle production. Global satellite-based monitoring of biomass burning using thermal infrared sensors is currently a powerful tool to assist in finding ways to establish suppression strategies and to understand the role that fires play in global climate change. Advances in silicon-based camera technology present opportunities to resolve the challenge of ubiquitous wildfire early detection in a cost-effective manner. This study investigated several feasibility aspects of detecting wildland fires using near-infrared (NIR) spectral line emissions from electronically excited potassium (K) atoms at wavelengths of 766.5 and 769.9 nm, during biomass burning.
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