## 2.3.2. Ground Albedos[¶](#ground-albedos "Permalink to this headline")
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The overall direct beam \\(\\alpha \_{g,\\, \\Lambda }^{\\mu }\\) and diffuse \\(\\alpha \_{g,\\, \\Lambda }\\) ground albedos are weighted combinations of “soil” and snow albedos

(2.3.58)[¶](#equation-3-58 "Permalink to this equation")\\\[\\alpha \_{g,\\, \\Lambda }^{\\mu } =\\alpha \_{soi,\\, \\Lambda }^{\\mu } \\left(1-f\_{sno} \\right)+\\alpha \_{sno,\\, \\Lambda }^{\\mu } f\_{sno}\\\]

(2.3.59)[¶](#equation-3-59 "Permalink to this equation")\\\[\\alpha \_{g,\\, \\Lambda } =\\alpha \_{soi,\\, \\Lambda } \\left(1-f\_{sno} \\right)+\\alpha \_{sno,\\, \\Lambda } f\_{sno}\\\]

where \\(f\_{sno}\\) is the fraction of the ground covered with snow (section [2.8.1](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/Snow_Hydrology/CLM50_Tech_Note_Snow_Hydrology.html#snow-covered-area-fraction)).

\\(\\alpha \_{soi,\\, \\Lambda }^{\\mu }\\) and \\(\\alpha \_{soi,\\, \\Lambda }\\) vary with glacier, lake, and soil surfaces. Glacier albedos are from [Paterson (1994)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#paterson1994)

\\\[\\alpha \_{soi,\\, vis}^{\\mu } =\\alpha \_{soi,\\, vis} =0.6\\\]

\\\[\\alpha \_{soi,\\, nir}^{\\mu } =\\alpha \_{soi,\\, nir} =0.4.\\\]

Unfrozen lake albedos depend on the cosine of the solar zenith angle \\(\\mu\\)

(2.3.60)[¶](#equation-3-60 "Permalink to this equation")\\\[\\alpha \_{soi,\\, \\Lambda }^{\\mu } =\\alpha \_{soi,\\, \\Lambda } =0.05\\left(\\mu +0.15\\right)^{-1} .\\\]

Frozen lake albedos are from NCAR LSM ([Bonan 1996](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#bonan1996))

\\\[\\alpha \_{soi,\\, vis}^{\\mu } =\\alpha \_{soi,\\, vis} =0.60\\\]

\\\[\\alpha \_{soi,\\, nir}^{\\mu } =\\alpha \_{soi,\\, nir} =0.40.\\\]

As in NCAR LSM ([Bonan 1996](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#bonan1996)), soil albedos vary with color class

(2.3.61)[¶](#equation-3-61 "Permalink to this equation")\\\[\\alpha \_{soi,\\, \\Lambda }^{\\mu } =\\alpha \_{soi,\\, \\Lambda } =\\left(\\alpha \_{sat,\\, \\Lambda } +\\Delta \\right)\\le \\alpha \_{dry,\\, \\Lambda }\\\]

where \\(\\Delta\\) depends on the volumetric water content of the first soil layer \\(\\theta \_{1}\\) (section [2.7.3](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/Hydrology/CLM50_Tech_Note_Hydrology.html#soil-water)) as \\(\\Delta =0.11-0.40\\theta \_{1} >0\\), and \\(\\alpha \_{sat,\\, \\Lambda }\\) and \\(\\alpha \_{dry,\\, \\Lambda }\\) are albedos for saturated and dry soil color classes ([Table 2.3.3](#table-dry-and-saturated-soil-albedos)).

CLM soil colors are prescribed so that they best reproduce observed MODIS local solar noon surface albedo values at the CLM grid cell following the methods of [Lawrence and Chase (2007)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#lawrencechase2007). The soil colors are fitted over the range of 20 soil classes shown in [Table 2.3.3](#table-dry-and-saturated-soil-albedos) and compared to the MODIS monthly local solar noon all-sky surface albedo as described in [Strahler et al. (1999)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#strahleretal1999) and [Schaaf et al. (2002)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#schaafetal2002). The CLM two-stream radiation model was used to calculate the model equivalent surface albedo using climatological monthly soil moisture along with the vegetation parameters of PFT fraction, LAI, and SAI. The soil color that produced the closest all-sky albedo in the two-stream radiation model was selected as the best fit for the month. The fitted monthly soil colors were averaged over all snow-free months to specify a representative soil color for the grid cell. In cases where there was no snow-free surface albedo for the year, the soil color derived from snow-affected albedo was used to give a representative soil color that included the effects of the minimum permanent snow cover.

<table id="id9"><caption><span>Table 2.3.3 </span><span>Dry and saturated soil albedos</span><a href="#id9" title="Permalink to this table">¶</a></caption> <colgroup><col> <col> <col> <col> <col> <col> <col> <col> <col> <col></colgroup><tbody><tr><td></td><td colspan="2"><p>Dry</p></td><td colspan="2"><p>Saturated</p></td><td></td><td colspan="2"><p>Dry</p></td><td colspan="2"><p>Saturated</p></td></tr><tr><td><p>Color Class</p></td><td><p>vis</p></td><td><p>nir</p></td><td><p>vis</p></td><td><p>nir</p></td><td><p>Color Class</p></td><td><p>vis</p></td><td><p>nir</p></td><td><p>vis</p></td><td><p>nir</p></td></tr><tr><td><p>1</p></td><td><p>0.36</p></td><td><p>0.61</p></td><td><p>0.25</p></td><td><p>0.50</p></td><td><p>11</p></td><td><p>0.24</p></td><td><p>0.37</p></td><td><p>0.13</p></td><td><p>0.26</p></td></tr><tr><td><p>2</p></td><td><p>0.34</p></td><td><p>0.57</p></td><td><p>0.23</p></td><td><p>0.46</p></td><td><p>12</p></td><td><p>0.23</p></td><td><p>0.35</p></td><td><p>0.12</p></td><td><p>0.24</p></td></tr><tr><td><p>3</p></td><td><p>0.32</p></td><td><p>0.53</p></td><td><p>0.21</p></td><td><p>0.42</p></td><td><p>13</p></td><td><p>0.22</p></td><td><p>0.33</p></td><td><p>0.11</p></td><td><p>0.22</p></td></tr><tr><td><p>4</p></td><td><p>0.31</p></td><td><p>0.51</p></td><td><p>0.20</p></td><td><p>0.40</p></td><td><p>14</p></td><td><p>0.20</p></td><td><p>0.31</p></td><td><p>0.10</p></td><td><p>0.20</p></td></tr><tr><td><p>5</p></td><td><p>0.30</p></td><td><p>0.49</p></td><td><p>0.19</p></td><td><p>0.38</p></td><td><p>15</p></td><td><p>0.18</p></td><td><p>0.29</p></td><td><p>0.09</p></td><td><p>0.18</p></td></tr><tr><td><p>6</p></td><td><p>0.29</p></td><td><p>0.48</p></td><td><p>0.18</p></td><td><p>0.36</p></td><td><p>16</p></td><td><p>0.16</p></td><td><p>0.27</p></td><td><p>0.08</p></td><td><p>0.16</p></td></tr><tr><td><p>7</p></td><td><p>0.28</p></td><td><p>0.45</p></td><td><p>0.17</p></td><td><p>0.34</p></td><td><p>17</p></td><td><p>0.14</p></td><td><p>0.25</p></td><td><p>0.07</p></td><td><p>0.14</p></td></tr><tr><td><p>8</p></td><td><p>0.27</p></td><td><p>0.43</p></td><td><p>0.16</p></td><td><p>0.32</p></td><td><p>18</p></td><td><p>0.12</p></td><td><p>0.23</p></td><td><p>0.06</p></td><td><p>0.12</p></td></tr><tr><td><p>9</p></td><td><p>0.26</p></td><td><p>0.41</p></td><td><p>0.15</p></td><td><p>0.30</p></td><td><p>19</p></td><td><p>0.10</p></td><td><p>0.21</p></td><td><p>0.05</p></td><td><p>0.10</p></td></tr><tr><td><p>10</p></td><td><p>0.25</p></td><td><p>0.39</p></td><td><p>0.14</p></td><td><p>0.28</p></td><td><p>20</p></td><td><p>0.08</p></td><td><p>0.16</p></td><td><p>0.04</p></td><td><p>0.08</p></td></tr></tbody></table>

