Multiband photometry of Martian Recurring Slope Lineae (RSL) and dust-removed features at Horowitz crater, Mars from TGO/CaSSIS color observations

Recurring Slope Lineae (RSL) are narrow, dark streaks typically lengthening down Martian steep slopes during warm seasons, fading during the cold ones and regularly recurring every Martian year. Their origin is still debated. Although initially interpreted as possible flows of seeping water, either coming from a subsurface aquifer or through atmospheric processes, recent studies favor a dry granular flow origin. To date, the nature and formation mechanism of RSL represent an open science question about present-day surface processes occurring on Mars. In this study, we analyze color observations of RSL at Horowitz crater, acquired with the Colour and Surface Science Imaging System (CaSSIS) on board ESA's ExoMars Trace Gas Orbiter (TGO) mission. We compare the relative photometry of RSL with respect to nearby terrains with the relative reflectance of dust-removed surfaces, including dust-devil tracks, in the four CaSSIS filters to help assess their properties. Comparing our relative photometry with dust-deposition and soil-wetting models coming from published laboratory experiments, we find that the former results provide a better fit to the observations than the latter, hence supporting a dry origin for Horowitz RS

In-flight radiometric calibration of the ExoMars TGO Colour and Stereo Surface Imaging System

The Colour and Stereo Surface Science Imaging System (CaSSIS) of the ExoMars Trace Gas Orbiter returns on average twenty images per day of the Martian surface, most of them in 3 or 4 colours and some of them in stereo. CaSSIS uses a push-frame approach to acquire colour images, with four bandpass filters deposited directly above the sensor and an imaging cadence synchronized with the ground track velocity to cover the imaged area with tens of small, partially overlapping images. These “framelets” are later map-projected and mosaicked to build the final image. This approach offers both advantages and challenges in terms of radiometric calibration. While the collection of dark and flatfield frames is considerably enhanced by the frequent and fast acquisition of tens of successive images, mosaics assembled from the adjacent framelets highlight the straylight and changes in the bias of the detector. Both issues have been identified on CaSSIS images, with low intensities overall (up to a few %), but sufficient to generate prominent artefacts on the final assembled colour images. We have therefore developed methods to correct these artefacts that are now included into the radiometric calibration pipeline. We detail here the different steps of the calibration procedure and the generation of the products used for calibration, and discuss the efficacy of the corrections. The relative uncertainties on the bias and flatfield frames are low, of the order of 0.2 and 0.1%, respectively. The uncertainty on the absolute radiometric calibration is of 3%, which is quite low for such an instrument. The straylight adds an estimated ∼1% error to the absolute calibration. The residuals after corrections of the straylight and bias offsets are of the order of a few DNs to tens of DNs. As CaSSIS can observe the Martian surface in challenging illumination conditions to provide unique views of the surface at early and late local solar time, residuals from the straylight correction can become noticeable when the absolute signal is very low. As they appear at the level of the noise in very low illumination images, these residuals do not limit the scientific exploitation of the data. For most of the dataset, as the signal in well-exposed images reaches 8000 DNs in the panchromatic filter and thousands of DNs in the colour filters, the residuals are negligible and CaSSIS provides the best colour images available over many areas covered

Chapter 14 Algae as a Potential Source of Biokerosene and Diesel – Opportunities and Challenges

In times of dwindling petroleum reserves, microalgae may pose an alternate energy resource. Their growth is vast under favorable conditions. However, producing microalgae for energy in an economically as well as ecologically feasible way is a difficult task and the prospects are challenging. The chapter gives an insight into perspectives of growing microalgae as a crop, highlighting some of their exceptional energy storage properties in regard to commercial exploitation. Large scale algae production techniques and concepts up to downstream processes are presented. Today, conversion to fuels is constrained by energy usage and costs – but future combination of fuel production with added value products may improve balances and lower the industrial CO2 footprint. These challenges drive research and industry worldwide to constant improvement, supported by numerous funding opportunities. Microalgae in their tremendous diversity are a young and still very much unexplored crop. It is a challenge worth addressing