Description: Extensive efforts are currently being devoted to the establishment of soil spectral libraries on regional, national, continent-wide and global domains. In particular, a new development goes in the direction of global harmonized soil spectral databases that shall be acquired following common standards and procedures so that they can be merged with other soil spectral libraries. The choice of standards is important, especially with respect to their behaviors when laboratory conditions, such as humidity, change. In this study, we test the application and robustness of the Internal Soil Standard (ISS) spectral re-alignment procedure on an extended number of soil samples acquired at different laboratories. In particular, a focus is placed on the comparison between two standards Lucky Bay (LB) and Wylie Bay (WB), for their performance with different humidity laboratory conditions. LB and WB are almost pure quartz sands from Australia. For this, 71 soil samples from Israel with different mineralogical background and variable soil organic matter contents are scanned at two laboratories. The scanning took place with different spectral measurement protocols and extreme diverse conditions in terms of laboratory humidity and moist. All scans are completed by the repeated scans of the two Australian white sands through all scan batches to harmonize the spectral measurements. Our results show that the ISS minimizes the visual spectral variation, aligns the minor and extreme systematic changes of the protocols, and makes them more stable. Furthermore, the LB and WB standards do not exhibit equal performance regarding to relatively dry and humid conditions. The WB standard provides more stable and satisfactory results in humid condition. However, the high performance of the LB sample in spectral correction is still observed, particularly in laboratories with lower moist. Accordingly, these analyses suggest that in the ISS re-alignment procedure, the WB sample is more reliable to be used in humid laboratory condition.

Description: Imaging spectroscopy (IS) has largely demonstrated its capabilities for the quantitative derivation of several top-soilproperties remotely. Upcoming spaceborne hyperspectral sensors that will be put in space in 2019-2020 (PRISMA,EnMAP, HISUI) and in the following years (e.g. SHALOM, the NASA mission SBG/HypsIRI, the ESA candidatemission CHIME) will open the way for the global mapping and monitoring of soils. Nonetheless, the potential ofIS for soil applications at large scale has not been yet fully exploited. In particular, an avenue of development istoward global harmonized soil databases such as global soil spectral libraries. These databases are crucial sincethey can allow the development of robust calibrations for the multivariate prediction of soil properties applicablefrom regional to global scale. To date there are many spectral libraries that are being developed at the country scale(e.g. France, Israel, Brazil, China, Australia, Denmark), at the continent scale (EU-wide LUCAS soil database), orat the global scale (World Soil Spectral Library of Viscarra-Rossel et al). One of the main issues in the developmentof such spectral libraries is about the use of standards and protocols and production of harmonized data bases sothat (i) data are controlled and reproducible, and (ii) current databases acquired at different locations with differentprotocols can be merged.In this study, we tested the application and robustness of the Internal Soil Standard (ISS) method for the spectralalignment and correction of spectral measurements on an extended number of soil samples acquired at differentlaboratories. Furthermore, we tested how the ISS commonly used sand standards, Lucky Bay (LB) and WylieBay (WB) samples, almost pure quartz sands from Australia, perform in different humidity laboratory conditions.Currently, most users of the ISS method use the LB sample. Then 71 soil samples from Israel with different miner-alogical background and variable soil organic matter contents were scanned at Tel-Aviv (TAU, Israel) and Potsdam(GFZ, Germany) laboratories. The scanning took place with different spectral measurement protocols and extremediverse conditions in terms of laboratory humidity and moist. All scans were completed by the repeated scansof the two Australian white sands through all scan batches to harmonize the spectral measurements. The resultsshowed that the ISS minimized the visual spectral variation, aligned the minor and extreme systematic changes ofthe protocols, and made them more stable. Also, it showed that the LB and WB did not exhibit equal performanceregarding to relatively dry and humid conditions. The WB standard provided more stable and satisfactory resultsin humid condition. However, the high performance of the LB sample in spectral correction was still obvious,particularly in laboratories with lower moist. Accordingly, these analyses suggested that during the ISS procedure,attention to the laboratory relative moist conditions must be taken, and in humid laboratory conditions, the WBsample is more reliable to be used than the LB sample.