# Remote Sensing Data for Digital Soil Mapping in French Research--A Review
## 2 General Considerations on the Relative Permanence of Soil Properties  
DSM predicts soil properties that may change over different times, from brief sudden events to millions of years. Time intervals vary with soil properties and processes and are highly dependent on the controlling factors for soil formation and anthropogenic influences. These factors can be rather slow, such as weathering and pedogenesis, or short-lived when related to destructive events, such as deforestation, erosion and flooding, or local contamination. RS technology has evolved rapidly over the last 50 years or so, providing greater diversity in spectral domains, but also a drastic increase in their spatial resolution and revisit time. This improves our understanding of the relative permanence of soil properties, yet it is limited to one week to half a century. In this section, we will refer mainly to the international literature, as many concepts have emerged outside the strict French soil science community. Soils are continually evolving over time, and the rate of change in soil properties is accelerating due to global changes and continued unsustainable land management [2; 4]. The \"natural\" formation time of soils, from the initial weathering of parent materials to pedogenic evolution, may range from about 10,000 to 2,500,000 years. As a result, the evolution and properties of natural soils mainly depend on age (time), climate (including past climates), parent material, and natural vegetation. It is generally accepted that the \"age\" factor is least used in DSM, except for some long periods of extreme climate (e.g., glaciation and interglacial periods) [16]. Therefore, the influence of past climate may be underestimated by DSM covariates and is often barely captured by RS products, as they do not cover the duration of most pedogenetic processes. Many soil properties have been affected by drastic changes since the impact of humans, especially by gradual or abrupt land-use changes. This began when humans moved from hunting and gathering to agriculture (Neolithic revolution). This then led to (ongoing) deforestation and the conversion of land to arable land, and more recently to global changes, such as anthropogenic climate change, industrialization, urbanization and increases in impervious surfaces, land-take, and changes in land use/land cover due to food demand. To differentiate the effects of long- and short-term periods on soil variability, researchers have proposed a distinction between genosoils and phenos Soils [115]. This concept makes it possible to distinguish certain semi-permanent properties inherited from \"natural\" pedogenesis from properties that have evolved under human pressure, especially for the history of land use. It has led to further development and discussions of which soil properties can be considered more or less \"permanent\", e.g., certain characteristics of deep diagnostic horizons [116], while others may change with land use, management (e.g., [117; 118; 119; 120]), or under other circumstances. This concept is quite similar to the concept of soil capability vs. soil condition, as defined by [PERSON] et al. [1]. In this study, we will therefore make the assumption that certain soil attributes can be considered permanent (e.g., soil texture, soil mineralogy, and parent material) on the time-scale of RS observations (i.e., 50 years). Unless there is evidence that abrupt or destructive events have occurred, such as severe erosion or salinization. The typical duration of the semi-permanent changes can range from decades to centuries (e.g., soil organic carbon stocks and diffuse contaminant contents) to seasonal ones (e.g., deep horizon structure and permeability, pH, rooting depth, and soil temperature). Much more rapid and/or even nearly instantaneous changes are related to human actions or climate events, e.g., local contamination, nutrients content, topsoil structure and roughness, pH in lined cultivated soils, and, of course, soil moisture.