Modeling three-dimensional forest structures to drive canopy radiative transfer simulations of bidirectional reflectance factor

Figures & data

Table 1. Estimation models of DBH, CL, and CR based on TH for the Järvselja site and PFRR site.

Site	Equations	R^2	Reference
Järvselja	DBH (cm) = 1.0398Exp(0.1795TH)	0.95	Kuusk et al. (2012)
	CL (m) = 0.3217Exp(0.1615TH)	0.78
	CR (m) = 0.0395Exp(0.2284TH)	0.89
PFRR	DBH (cm) = 1.95ln(TH) − 0.37	0.93	Kobayashi et al. (2014)
	CL (m) = TH − 0.48	1.00
	CR (m) = 0.0875ln(TH) + 0.3109	0.92

Figure 1. Four different crown shapes and the parameters used to define them (DBH, diameter at breast height; TH, tree height; CL, crown length; and CR, crown radius).

Figure 2. Framework of the proposed Forest Structure Model (FSM) used to generate a simulated forest stand.

Table 2. Input parameter to the FLiES model.

Parameter	PFRR site	Järvselja site
LAI	0.73	2.21
Spherical average shoot silhouette to total area ratio^a	0.158	0.158
Needle reflectance	(0.058, 0.428, 0.052, 0.116, 0.387, 0.252, 0.235)^b	(0.058, 0.428, 0.052, 0.116, 0.387, 0.252, 0.235)^b
Needle transmittance	(0.037, 0.390, 0.021, 0.087, 0.372, 0.237, 0.000)^b	(0.037, 0.390, 0.021, 0.087, 0.372, 0.237, 0.000)^b
Stem reflectance	(0.225, 0.461, 0.147, 0.210, 0.606, 0.582, 0.264)^b	(0.225, 0.461, 0.147, 0.210, 0.606, 0.582, 0.264)^b
Floor reflectance	(0.124, 0.280, 0.062, 0.086, 0.376, 0.297, 0.178)^b	(0.124, 0.280, 0.062, 0.086, 0.376, 0.297, 0.178)^b
Forest landscape	Generated by the proposed approach of this study	Generated by the proposed approach of this study

^aFrom Kobayashi et al. (2010).

^bValues for MODIS bands 1–7.

Figure 3. Statistical distributions of TH at the (a) Järvselja and (b) PFRR sites, compared to the Weibull distributions.

Figure 4. Statistical distributions of tree locations at the (a) Järvselja and (b) PFRR sites, obtained by dividing the measurement plot into 100 quadrats, and then compared to the Poisson and Neyman distributions.

Figure 5. Vertical view of (a) the modeled forest stand, and (b) the measured stand at the Järvselja site; (c) the modeled forest stand and (d) the measured stand at the PFRR site. CC, crown coverage.

Table 3. Descriptive statistics of the structural parameters of the measured and modeled forest stands at the Järvselja and PFRR sites.

	TH (m)	CL (m)	CR (m)	DBH (cm)	TD (ha^−1)	CC (%)
Järvselja_measured	15.48 (1.51)	4.05 (1.01)	1.44 (0.47)	17.34 (4.44)	1121	62.91
Järvselja_modeled	14.85 (1.45)	3.57 (0.93)	1.22 (0.42)	15.39 (3.93)	1121	49.74
PFRR_measured	2.44 (1.07)	1.96 (1.07)	0.38 (0.04)	2.42 (1.59)	3967	14.89
PFRR_modeled	2.42 (1.33)	1.94 (0.76)	0.38 (0.04)	1.48 (0.76)	3967	17.11

Notes: TH, tree height; CL, crown length; CR, crown radius; DBH, diameter at breast height; TD, tree density; and CC, crown coverage. Values in brackets are standard deviations.

Table 4. Performance assessment of the proposed method for deriving RT simulations of BRF of forest stand.

		Järvselja		PFRR
		SZA = 40°	SZA = 60°	SZA = 40°	SZA = 60°
Red	R^2	0.99	0.99	0.99	0.99
	RMSE	0.006	0.005	0.002	0.002
	rRMSE (%)	19.02	19.82	2.24	2.63
NIR	R^2	0.99	0.99	0.99	0.99
	RMSE	0.005	0.008	0.002	0.005
	rRMSE (%)	2.72	3.32	0.81	2.16
SWIR	R^2	0.99	0.99	0.99	0.99
	RMSE	0.006	0.006	0.002	0.004
	rRMSE (%)	2.69	2.49	0.74	1.6

Figure 9. Comparison of MODIS and simulated BRF for (a) the Järvselja site and (b) the PFRR site.

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