Forest 2200 nm/660 nm reflectance seasonality for improved satellite-image atmospheric correction

Construction rules for tree-species groups. The fertility classes correspond to Orlov’s bonity categories, where 0 indicates the greatest and 6 the lowest fertility. The bonity class 3 is excluded from soil fertility-dependent subsets. Forest inventory data do not distinguish between silver birch and downy birch. However, it is known that downy birch dominates on poor soils.

Group	Species	Share(%)	Fertility classes
All stands	All	All	all
Evergreen needleleaved	Norway spruce, Scots pine	>85	all
Deciduous broadleaved	Norway spruce excluded, Scots pine excluded	≥85	all
Pine	Scots pine	≥80	all
Pine (fertile soil]	Scots pine	≥ 80	0,1,2
Pine (poor soil)	Scots pine	≥80	4,5,6
Birch spp.	Silver birch, downy birch	≥80	all
Birch (fertile soil)	Silver birch	≥80	0,1,2
Birch (poor soil)	(Silver birch), downy birch	≥80	4,5,6
Spruce	Norway spruce	≥80	all
Aspen	European aspen	≥75	all
Alder	Grey alder	≥75	all

Table 2.

Detailed descriptions of the tree species groups introduced in Table 1. KU signifies Norway spruce, MA Scots pine, HB European aspen, KS both silver birch and downy birch (these two species are not distinguished in the forest inventory of the Estonian Environment Agency), LV grey alder, and KX species compositions not matching any of the other codes. Stands in the evergreen needleleaf group Everg. N. consist predominantly of Norway spruce and Scots pine, while stands in the group Dec. Br. are dominated by deciduous broadleaved species. In the Bon (bonity) column, code A signifies all fertility classes, P poor soils, and F fertile soils. For each tree species group, an entry in the N column gives the number of stands in that group, S its aggregate area, A the mean value of its various stand ages, H₁₀₀ the mean value of the 100-year heights predicted for its various stands (this is a measure of site productivity), T its relative density, and G its basal area.

Group	Stands			Stand structure				Tree species composition (%)
Species	Bon	N	S (ha)	A	H₁₀₀ (m)	T (%)	G (m²ha⁻¹)	HB	KS	KU	LV	MA	KX
All	A	92,230	231,687	77	26.6	94	28.4	6	29	26	3	33	3
Everg. N.	A	34,073	83,321	92	25.4	92	30.4	0	4	28	0	68	0
Dec. Br.	A	22,659	60,990	61	27.1	95	25.4	13	60	9	8	1	9
MA	A	1,5898	39,765	94	23.4	90	29.7	0	3	5	0	92	0
MA	F	8,675	20,553	85	27.2	91	31.1	0	3	7	0	90	0
MA	P	3,388	9,575	107	15.8	89	26.6	0	3	2	0	95	0
KU	A	5,092	11,627	51	31.3	93	27.7	1	6	90	1	1	1
KS	A	6,471	17,024	56	24.8	93	21.7	1	90	4	1	2	2
KS	F	4,013	10,130	50	27.3	93	22.6	1	90	5	1	1	2
KS	P	6,66	1,978	69	17.6	94	18.5	0	91	2	0	4	3
HB	A	441	951	65	31.7	95	31.7	83	8	6	1	0	2
LV	A	960	2,222	45	27.0	96	25.8	2	5	3	88	0	2

The average seasonal course of the red ρ_0.6 and near-infrared ρ_2.2 reflectance ratio, summarised as a boxplot using 5-day bins. The dashed line corresponds to the preliminary model estimated from USGS Landsat-8/9 OLI L2 surface reflectance data. The wide line corresponds to model (1); the narrower line to our spline-based refinement.

Table 3.

Estimated parameters for the model (1). An observation is one stand on an image granule. RSE is the model residual error. R² is the determination coefficient as defined by equation (2). Parameter values in the shaded cells were not significant. The parameter c has been fixed to the constant c = 1.

Model for group	N. obs	R²	RSE	Parameter estimates
Model for group	N. obs	R²	RSE	a	b	d	k_pk	k_k	k_ps	k_s
All	5.6 × 10⁶	0.15	0.69	2.22	2.22	1.24	140.0	5.84	262.4	22.0
Evergreen needleleaf	2.2 × 10⁶	0.02	0.47	2.21	39.2	6.52	140.0	5.03	270.9	22.0
Deciduous broadleaf	1.4 × 10⁶	0.45	0.68	2.34	1.22	0.95	138.0	4.50	255.0	25.0
Scots pine (MA)	1.0 × 10⁶	0.05	0.43	2.20	160.0	5.61	136.9	4.00	262.3	21.0
MA (fertile soil)	6.3 × 10⁵	0.05	0.43	2.21	160.0	5.41	141.0	4.45	264.7	23.0
MA (poor soil)	6.3 × 10^s	0.04	0.44	2.17	99.9	6.83	140.0	4.61	261.8	22.0
Norway spruce (KU)	6.3 × 10⁵	0.02	0.56	2.19	5.55	6.13	150.0	8.00	280.0	22.0
Birch spp. (KS)	6.3 × 10⁵	0.46	0.63	2.29	1.23	0.90	135.0	4.00	255.0	25.0
KS (fertile soil)	6.3 × 10⁵	0.46	0.64	2.31	1.25	0.90	135.0	4.00	255.0	25.0
KS (poor soil)	6.3 × 10⁴	0.45	0.66	2.24	1.19	0.90	137.4	4.00	255.0	25.0
European aspen (HB)	3.5 × 10⁴	0.47	0.67	2.35	1.09	0.90	138.0	4.20	250.0	22.0
Grey alder (LV)	4.3 × 10⁴	0.49	0.61	2.36	0.82	0.90	131.0	9.27	257.5	18.9

Evergreen needleleaf tree species group. Figure details are as in Figure 1.

Deciduous broadleaved tree species group. Figure details are as in Figure 1.

Table A2.1.

Smoothed course of the near-infrared/red reflectance ratio ρ_2.2/ρ_0.6. Values are scaled by 100. Group descriptions are given in Tables 1 and 2.

Day	Tree species groups
Day	All	Everg. N.	Dec. Br.	MA-A	MA-F	MA-P	KU-A	KS-A	KS-F	KS-P	HB-A	LV-A
70	226	223	226	224	228	220	224	225	222	229	233	246
73	226	223	228	223	227	220	225	229	227	229	233	246
76	226	222	230	222	226	219	225	231	231	228	233	245
79	225	222	231	222	225	218	225	232	232	226	232	245
82	224	222	230	221	224	218	224	231	232	224	231	245
85	223	222	229	221	223	217	222	229	229	223	231	244
88	222	222	227	220	222	216	220	226	226	221	230	244
91	222	222	226	220	222	216	219	224	224	221	230	243
94	221	222	227	220	221	216	218	224	224	223	230	243
97	221	222	228	220	221	216	219	226	226	224	231	243
100	221	222	230	220	221	217	220	229	229	226	232	243
103	222	222	232	220	221	217	220	232	232	227	233	244
106	222	222	232	220	221	217	220	233	233	227	233	245
109	222	222	231	220	221	217	219	231	231	226	232	246
112	223	222	230	220	222	218	219	230	230	224	231	248
115	223	222	229	221	222	218	219	229	229	222	229	251
118	225	222	229	221	222	219	220	228	229	222	228	254
121	227	222	231	221	223	219	222	230	231	222	229	259
124	229	222	234	221	223	219	224	234	236	224	233	265
127	232	222	240	221	223	220	225	239	242	228	239	272
130	236	222	250	221	223	219	226	248	252	235	250	280
133	241	222	265	221	222	219	227	262	267	246	266	289
136	245	222	281	221	222	219	229	278	283	261	285	298
139	250	223	296	220	221	218	231	293	297	275	302	308
142	253	223	307	220	220	217	232	304	307	287	316	316
145	256	223	314	219	220	217	233	311	313	293	326	324
148	258	223	316	219	220	217	234	312	314	296	330	330
151	260	223	314	219	220	217	234	308	310	296	330	336
154	260	223	312	219	220	217	233	304	307	295	329	340
157	261	223	312	219	220	217	232	304	306	297	330	343
160	261	223	314	219	220	217	232	309	310	302	331	345
163	262	223	318	219	220	217	233	315	316	308	332	347
166	262	223	321	219	220	217	234	319	320	312	333	349
169	262	223	320	219	220	217	234	317	318	311	332	350
172	262	223	318	218	219	217	234	312	312	308	330	351
175	262	223	315	218	219	216	234	307	308	304	328	352
178	262	223	313	218	219	216	233	304	305	303	327	353
181	262	223	313	218	218	215	233	306	307	304	326	354
184	263	223	315	218	218	215	232	312	313	307	326	356
187	264	223	317	218	218	215	232	317	318	310	326	357
190	264	223	318	219	219	216	232	318	320	310	325	359
193	266	222	318	219	219	216	234	315	318	307	324	361
196	267	222	318	219	220	217	236	311	314	304	323	363
199	268	222	319	220	220	218	238	310	312	302	323	364
202	269	222	320	220	221	219	241	311	313	302	324	365
205	269	222	322	220	222	219	243	312	314	304	326	364
208	269	221	323	220	222	220	245	314	315	307	328	363
211	269	221	324	220	222	220	247	317	317	311	328	362
214	268	220	325	220	222	221	247	320	319	315	328	360
217	267	220	323	219	222	221	246	320	319	316	325	357
220	265	219	320	219	221	220	244	316	315	313	321	353
223	262	218	315	218	220	219	242	311	311	309	317	349
226	259	218	311	216	219	218	240	305	306	302	312	345
229	255	217	306	215	217	216	237	300	302	294	307	341
232	251	216	299	213	215	214	234	293	296	285	301	336
235	247	215	291	211	213	211	231	283	286	276	294	331
238	242	214	282	209	211	208	228	274	276	269	287	326
241	239	214	275	208	209	206	226	266	267	263	282	321
244	235	213	269	206	207	203	224	261	261	258	278	316
247	232	212	264	204	206	201	224	257	256	255	275	312
250	230	212	259	203	205	199	224	252	251	252	273	308
253	228	211	256	202	204	198	225	249	249	249	271	305
256	226	211	254	201	203	197	227	247	247	246	270	303
259	224	211	253	200	202	197	229	244	245	243	268	301
262	223	211	252	200	201	197	230	242	242	239	265	300
265	221	211	250	200	200	197	231	239	239	236	258	298
268	219	211	246	200	200	199	232	236	237	233	248	296
271	216	211	240	201	201	201	233	234	233	231	235	292
274	213	211	230	203	202	203	232	228	227	227	220	288
277	209	212	217	204	203	206	228	216	213	221	204	282
280	205	212	201	206	205	209	219	199	193	212	189	276
283	202	213	186	208	206	212	210	182	174	204	177	268
286	199	213	176	211	209	215	204	171	161	199	171	260
289	198	214	173	214	212	219	202	170	159	200	170	253
292	200	215	177	217	216	224	206	179	166	206	175	245
295	202	216	184	221	221	230	213	192	178	215	183	237
298	207	217	194	225	227	236	225	204	190	224	193	230
301	212	218	205	229	233	243	239	215	202	233	204	222
304	217	218	216	233	239	250	254	225	212	241	215	215
307	223	219	227	238	246	257	269	235	223	249	226	208
310	228	220	238	242	252	263	284	245	234	257	237	200

Table A3.1.

The normalised difference vegetation index I_NDVI = (ρ_0.85 – ρ_0.6) / (ρ_0.85 + ρ_0.6) mean values and standard deviation for our species groups. Spectral reflectances are from the bands at 0.85 μm (ρ_0.85) and 0.6 μm (ρ_0.6). Group descriptions are given in Tables 1 and 2. The estimate is made for the period starting from day 141 and ending with day 259.

Tree species group		NDVI
Species	Bonity	Mean	Standard deviation
All	A	0.79	0.09
Everg. N.	A	0.78	0.06
Dec. Br.	A	0.78	0.13
MA	A	0.77	0.06
MA	F	0.78	0.06
MA	P	0.76	0.06
KU	A	0.82	0.07
KS	A	0.77	0.13
KS	F	0.78	0.13
KS	P	0.75	0.15
HB	A	0.78	0.15
LV	A	0.79	0.14

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DOI: https://doi.org/10.2478/fsmu-2025-0001 | Journal eISSN: 1736-8723 | Journal ISSN: 1406-9954

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Language: English

Page range: 1 - 19

Submitted on: Feb 6, 2025

Accepted on: Aug 12, 2025

Published on: Mar 23, 2026

Published by: Estonian University of Life Sciences

In partnership with: Paradigm Publishing Services

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© 2026 Mait Lang, Lea Hallik, Allan Sims, published by Estonian University of Life Sciences
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

Volume 82 (2025): Issue 1 (December 2025)

Forest 2200 nm/660 nm reflectance seasonality for improved satellite-image atmospheric correction

Figures & Tables

Table 1.

Table 2.

Figure 1.

Table 3.

Figure 2.

Figure 3.

Figure A1.1.

Figure A1.2.

Figure A1.3.

Figure A1.4.

Figure A1.5.

Figure A1.6.

Figure A1.7.

Figure A1.8.

Figure A1.9.

Table A2.1.

Table A3.1.

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