# Review of Land Surface Albedo: Variance Characteristics, Climate Effect and Management Strategy
## 2 Literature Analysis of Surface Albedo
### Definition Distinction
\[\text{BSA}(\theta_{i},\lambda)=\frac{1}{\pi}\int_{0}^{2\pi}\int_{0}^{\frac{ \pi}{2}}R(\theta_{i},\theta_{v},\varphi,\lambda)\sin\theta_{v}\cos\theta_{v}d \theta_{v}d\varphi \tag{2}\]  
\[\text{WSA}(\lambda)=2\int_{0}^{\frac{\pi}{2}}\text{BSA}(\theta_{i},\lambda) \sin\theta_{i}\cos\theta_{i}d\theta_{i} \tag{3}\]  
\[\alpha(\theta_{i},\lambda)=(1-S(\theta_{i},\tau(\lambda)))\text{BSA}(\theta_ {i},\lambda)+S(\theta_{i},\tau(\lambda))\text{WSA}(\lambda) \tag{4}\]  
\[\alpha_{sw}(\theta_{i},\Lambda)=\frac{\int_{\lambda_{1}}^{\lambda_{2}}F_{d} (\theta_{i},\lambda)\alpha(\theta_{i},\lambda)d\lambda}{\int_{\lambda_{1}}^{ \lambda_{2}}F_{d}(\theta_{i},\lambda)d\lambda} \tag{5}\]  
Then, shortwave radiative forcing from surface albedo change can be calculated to evaluate its climate effect [29]. Given the asymmetry between solar irradiance and the seasonal cycle of surface albedo in many extratropical regions, the local annual mean instantaneous shortwave radiative forcing \(RF_{\Delta\alpha}\) at TOA (in W/m\({}^{2}\)) is usually estimated following monthly surface albedo changes. One method is to use radiative kernels derived from global climate models [41] although they are model- and state-dependent, and a simplified \(RF_{\Delta\alpha}\) model allowing greater flexibility surrounding the prescribed atmospheric state has recently been presented as Equation (6) [42]: where \(\Delta\alpha_{m}\), \(F_{d}\hat{s}_{m}\), and \(T_{m,t}\) refer to a surface albedo change, the incident solar irradiance at surface level, and the all-sky monthly mean clearness index in month m and year \(t\), respectively. We can see that a negative value can be obtained as surface albedo increases, which shows a cooling effect to offset CO\({}_{2}\) emission. In turn, reduced surface albedo means the exacerbation of warming effect. This circulation is always called surface albedo feedback [27]. Considering importance of snow and sea ice with high albedo, feedbacks over these two kinds of surfaces have been widely studied, which are called as snow albedo feedback (SAF) [27] and sea-ice albedo feedback (SIAF) [32]. Meanwhile, the impact of albedo feedback on climate change is always focused on, and thus the word \"climate feedback\" is also widely used [43]. \[RF_{\Delta\alpha}(t)=\frac{1}{12}{\sum_{m=1}^{12}}\left(-{F_{d}}^{s}_{m,t}\sqrt{T _{m,t}}\Delta\alpha_{m,t}\right) \tag{6}\]  
During literature retrieval, we found that some similar albedo variables may have created confusion. The fraction of incoming solar energy scattered back to space by Earth is referred to as planetary albedo, which is also called Earth albedo or TOA albedo [44; 45]. Single scattering albedo (SSA) is generally associated with particles, where atmospheric aerosols near the surface, tropopause and TOA have attracted much attention [46]. Cloud albedo is also called plane parallel albedo and can be mainly affected by cloud-condensation nuclei of dimethyl sulphide, which is produced by marine phytoplankton and chemically oxidizes in the atmosphere to form sulphate aerosols [47; 48]. In addition, albedos for special surfaces have also been examined, such as albedos of water bottom [49] and exoplanets [50]. Meanwhile, albedos at special wavelengths have also been investigated [51]. Different from most satellite observations with a passive remote sensing mode depending on solar illumination, an object's albedo from an active light source is also widely used, such as the neutron albedo of a person [52] and metals [53]. In particular, the albedo tissue of fruit peels is extensively used in the food industry [54], especially that from citrus. Planetary albedo can significantly affect surface temperature [55], and both atmospheric and surface albedos contribute to planetary albedo [56]. Novel stratospheric aerosol injections have been proposed to increase planetary albedo and mitigate global warming [57]. Similarly, the influence of surface albedo variances on planetary albedo needs to be studied in the future.