Development of Forest Canopy Density Mapping and Monitoring Model using Indices of Vegetation, Bare soil and Shadow
3.Obtaining of Four(4) Indices
a. Advanced Vegetation Index (AVI)
When assessing the vegetation status of forests, the new methods first examine the characteristics of chlorophyll-a using a new Advanced Vegetation Index (AVI) that is calculated with the following formulae.
B1~B7: TM Band 1~7 data
B43=B4-B3 after normalization of the data range.
CASE-a B43<0 AVI= 0
CASE-b B43>0 AVI=((B4+1)x (256-B3) x B43)1/3
b. Bare Soil Index (BI)
The value of the vegetation index is not so reliable in situations where the vegetation covers less than half of the area. Fore more reliable estimation of the vegetation status, the new methods include a bare soil index (BI) which is formulated with medium infrared information. The underlying logic of this approach is based on the high reciprocity between bare soil status and vegetation status. By combining both vegetation and bare soil indices in the analysis, one may assess the status of forest lands on a continuum ranging from hi vegetation conditions to exposed soil conditions.
B1=((B5+B3)-(B4+B1)) / ((B5+B3) + (B4+B1)) x 100 +100
; 0<BI <200
The range of BI is covered within 8 bits range]
c. Shadow index (SI)
One unique characteristic of a forest is its three dimensional structure To extract information on the forest structure from RS data, the new methods examine the characteristics of shadow by utilizing (a) spectral information on the forest shadow itself and (b ) thermal information on the forest influenced by shadow.
The shadow index is formulated through extraction of the low radiance of visible bands.
SI=((256-B 1)x (256-B2) x (256-b3))
1/3
d. Thermal Index (TI)
Two (s) factors account for the relatively cool temperature inside a forest. One is the shielding effect of the forest canopy which blocks and absorbs energy from the sun. The other is evaporation from the leaf surface which mitigates warming. Formulationof the thermal index is based on these phenomenon. The source of thermal information is the infrared band of TM data.
4. The Procedure of FCD Model
The flowchart of the procedure for FCD mapping model are illustrated in Fig.2. Image processed result corresponding to the flowchart shows in fig.3.
Fig. 2 Flow chart of FCD Mapping Model
Fig. 3 Procedure of FCD (Forest Canopy Density) Mapping Model
a. Noise Reduction; Clouds, cloud shadow and water area
Clouds have a higher irradiance value than ground data. Moreover, the amount of irradiance varies depending on whether the clouds are white, gray, black or combinations of different shades. These factors adversely influence statistical treatment and analysis of imagery data. Furthermore, cloud shadow can be confused with shadow cast by adjacent mountains, These problems can be minimized by creating a cloud shadow mask, using a histogram based on data derived from TM band 1,2 and 3. Thereafter, a shadow mask of the mountain shadow area s formed at the ground level. This is done through parallel transformation of the mask of the cloud area. Water bodies create similar problems. Since water absorbs near infrared, water bodies should (and can) also be masked using a histogram of TM Band4.
