# Detecting Lithium (Li) Mineralizations from Space: Current Research and Future Perspectives
## 3 Future Perspectives
### Data Products Used for the Research  
Past applications (Section 2.1) included products such as ASTER, Landsat-5, Landsat-8, and Sentinel-2 images. For the purpose of this review, we will only consider the more recent products since our goal is to help in choosing the best product for future studies. The ASTER is an imaging instrument onboard of Terra satellite, the flagship satellite of NASA's Earth Observing System (EOS), launched in December 1999 [80]. It resulted from a collaboration between NASA and Japan's Ministry of Economy Trade and Industry--METI [80]. ASTER captures medium-high spectral resolution data in 14 bands whose spatial resolution varies with wavelength: 15 m in the VNIR, 30 m in the SWIR, and 90 m in the TIR [81]. ASTER also provides a stereo viewing capability for digital elevation model creation [80; 81]. The temporal resolution is 16 days. Due to sensor failure, SWIR data acquired since April of 2008 is not available [82]. Nonetheless, as mentioned before, ASTER's specific characteristics greatly contributed to mineral exploration, especially in alteration mapping associated with gold and porphyry copper deposits [53; 54]. A review of the different \"on-demand\" ASTER products can be found in the work of [PERSON] and [PERSON] [83]. The Landsat program represents the world's longest continuously acquired collection of space-based moderate-resolution multispectral land remote sensing data [84]. It is the result of a joint effort of the United States Geological Survey (USGS) and the National Aeronautics and Space Administration (NASA). Until now, Landsat counts with seven successful and one failed mission [84]. The last mission corresponds to Landsat-8, which was launched in 2013. Landsat-9 is planned to be launched in December 2020 [84]. Landsat-8 carries two different instruments: (i) the Operational Land Imager (OLI); and (ii) the Thermal Infrared Sensor (TIRS). Each image product contains nine spectral bands with a spatial resolution of 30 m for bands 1-7 and 9, and 15 m for band 8 (panchromatic); and two thermal bands (10 and 11) are collected at 100 m, but resampled for 30 m [85]. Each band consists of a 16-bit grayscale image. The scene size is 170 km \(\times\) 185 km [85]. The temporal resolution is 16 days. Key publications in geological remote sensing (at least until the time of publication) from both the Landsat and the ASTER eras can be found in [PERSON] et al. [53]. The Sentinel-2 mission includes the recent twin satellites Sentinel-2A and Sentinel-2B launched in the frame of the European Union's Copernicus Program [86]. Since the satellites are out of phase with each other, the temporal resolution is five days at the equator [87]. Both satellites acquire information in 13 spectral bands in the VNIR-SWIR regions: four bands at 10 m spatial resolution, six bands at 20 m, and three bands at 60 m [87]. The orbital swath width is 290 km. A comparison between Landsat-8, Sentinel-2 and ASTER bands is established in Table 2 and in Figure 2.  
[PERSON] et al. [53] refer to the importance of the Sentinel-2 mission to ensure data continuity, especially after the failure of ASTER's SWIR module. However, the application of Sentinel-2 images for geological studies is scarce when compared to the previously mentioned satellite sensors, especially when it comes to geological exploration. The first articles in the literature regarding this satellite address their potential to alteration and iron/gossan mapping, while others highlight the correspondence between ASTER, Landsat 8, and Sentinel-2 VNIR and SWIR bands [90; 91; 92; 93]. More recent studies highlight the possible contribution and suitability of Sentinel-2 images for geological mapping [94; 95] and for geological fault detection [96]. [PERSON] et al. [97] applied different MLAs, Artificial Neural Network (ANN), k-Nearest Neighbor (k-NN), RF and SVM, to Sentinel-2 images in order to perform lithological classification in an ophiolite complex in Inner Mongolia, China. [PERSON] et al.