Gaussian Noise Removal for Wet Chemistry Data from the Phoenix Mission

Introduction: The initial in-situ chemical analysis of the four soil samples delivered to the Wet Chemistry Laboratory (WCL) provided concentrations of the soluble ionic species in the soil along with the pH and conductivity. Even though at first the results appeared to present a simple picture of the soluble soil chemistry , it has become clearly evident that the analyses were complicated by an unplanned titration of the soil/water mixture with barium chloride, the presence of chemical species whose signal was convoluted into other sensor readings, and the effects of temperature and noise. The combined effect of these interferences has put into question the concentrations and identity of the ionic species that were directly measured. Use of such incorrect values in conjunction with chemical speciation modeling programs will result in misinterpretation of the parent salt composition of the soil analyzed by the Phoenix WCL. The WCL on board the phoenix lander performed the first comprehensive wet chemical analysis of the soil on Mars, during the summer of 2008. Each WCL consisted of a lower cell whose walls were lined with an array of sensors and an upper assembly for adding water, reagents, soil, and stirring. The sensor array included ion selective electrodes (ISE) for K