Detection of Water and Water Bearing Minerals from 10 M Distance under Bright Condition Using Remote Raman System

Overview: Detection of water and carbon is important in order to support existence of life on other planets. Water has been detected on Mars and Moon in the form of ice and in hydrous minerals. Among the various techniques to detect water, ice, and H 2 O/OH bearing minerals, Raman spectroscopy stands out as providing distinctive spectra for unambiguous identification of water and water bearing minerals. A portable remote Raman instrument developed at the University of Hawaii has been shown earlier to detect carbon in carbonate form in calcite, magnesite, dolomite, siderite etc. from distances of several meters in matter of seconds [1-3]. The Remote Raman system is shown here to detect water, ice, and water bearing minerals from a distance of 10 m under bright conditions with short integration time. The ability to detect water and other minerals from remote distances during daytime would be promising for analyzing targets at hard to reach places such as lakes, cliffs, craters etc. Introduction: Recently a portable remote Raman system developed at the University of Hawaii has been tested to obtain Raman spectra of minerals and organ-ics from distances ranging from 10 to 100 m in daylight condition [1-2]. Minerals with various functional groups such as carbonate, oxides, silicates, sul-fates, nitrates and phosphates were identified from the Raman spectra aquired with a single laser pulse excita-tion [3]. The single shot-spectra collected under illuminated condition and 1 µs integration time, show clear Raman features. In order to measure Raman spectra in daylight or under a well illuminated background , it is important to use a pulse laser source and a gated detector [1-3]. Such a combination significantly improves the signal to background ratio of the Raman peaks which have very weak cross-sections in comparison to Rayleigh or Mie scattering cross-section. Gated system also helps in reducing long-lived fluorescent background generated by inorganic fluorescent impurities, e.g., transition ions and rare-earth ions [4-7]. Raman spectra of water, ice, and various water bearing minerals such as gypsum (CaSO 4 .2H 2 O), chal-canthite (CuSO 4 .5H 2 O), bischofite (MgCl 2 .6H 2 O), epsomite (MgSO 4 .7H 2 O), melanterite (FeSO 4 .7H 2 O), rozenite (FeSO 4 .4H 2 O), szomolnokite (FeSO 4 .1H 2 O), sinjarite (CaCl 2 .2H 2 O), and hydrous sodium phosphates NaH 2 PO 4 .2H 2 O, Na 3 PO 4 .12H 2 O were measured from a …