Monitoring land surface and cover in urban and peri-urban environments using digital aerial photography

Figures & data

Figure 1. (Left) The extent of the study area is depicted by the green boundary overlaid on the satellite image of the greater Perth region. (Right) Urban areas are dynamic, as demonstrated by this three-date NDVI composite with the NDVI from 1990, 1998 and 2008 displayed in red, green and blue, respectively. Areas having shades of grey are stable in this display, hot colours represent vegetation decline and cool colours represent vegetation gain.

Figure 2. Primary monitoring data consist of radiometrically calibrated true orthophotos. Digital surface models are generated for each time epoch. Shown are examples of the DSM for 2007 and 2009 (left and middle) and a local example of the orthophoto and corresponding DSM (bottom and top right, respectively).

Table 1. The accuracy assessment of elevation differences between the DSM and triangulated tie points, and the DSM and independent check points.

	Triangulation tie points		Independent check points
Block names	Points	RMS (m)	Points	RMS (m)
Gnangara	383,489	0.182	453	0.457
Perth	518,802	0.246	16,348	0.393
Woorooloo	50,291	0.238	320	0.440
Wungong	10,786	0.264	26	0.334
South	327,858	0.198	1794	0.428
Rottnest	2402	0.319	37	0.346

RMS, root mean squared error.

Figure 3. Radiometric calibration of the aerial imagery. (a) Before calibration and (b) after calibration. Reflectance estimates were within 4.4, 9.9 and 18.7% of absolute reflectance as recorded for the black, grey and white painted targets, respectively (Collings and Caccetta 2013).

Figure 4. Depiction of the vegetation height for the year 2007 overlaid on a grey scale aerial photograph. In this figure, the height of the vegetation is indicted by its brightness in green, ordered from dark to bright green representing low to high vegetation height, respectively.

Table 2. Vegetation accuracy for the year 2007.

		Manual interpretation
Class label		Non-veg	Veg	Total	Users (%)
Site 1	Non-veg	158	8	166	95
	Veg	6	88	94	94
	Total	164	96	260
	Producers (%)	96	92		Overall = 95
Site 2	Non-veg	740	49	789	94
	Veg	7	132	139	95
	Total	747	181	928
	Producers (%)	99	73		Overall = 94
Site 3	Non-veg	167	4	171	98
	Veg	4	56	60	93
	Total	171	60	231
	Producers (%)	98	93		Overall = 97

The overall accuracy of the classifier compared with manual interpretation was above 94% for the three sites.

Table 3. Vegetation accuracy for the year 2009.

		Manual interpretation
Class label		Non-veg	Veg	Total	Users (%)
Site 1	Non-veg	165	16	181	91
	Veg	0	79	79	100
	Total	165	95	260
	Producers (%)	100	83		Overall = 94
Site 2	Non-veg	673	60	733	92
	Veg	33	162	195	83
	Total	706	222	928
	Producers (%)	95	73		Overall = 90
Site 3	Non-veg	172	3	175	98
	Veg	2	54	56	96
	Total	174	57	231
	Producers (%)	99	95		Overall = 98

The overall accuracy of the classifier compared with manual interpretation was above 90% for the three sites.

Table 4. Tree accuracy for the year 2007.

		Manual interpretation
Class label		Non-tree	Tree	Total	Users (%)
Site 1	Non-tree	186	22	208	89
	Tree	4	48	52	92
	Total	190	70	260
	Producers (%)	98	69		Overall = 90
Site 2	Non-tree	781	68	849	92
	tree	1	78	79	99
	Total	782	146	928
	Producers (%)	100	53		Overall = 93
Site 3	Non-tree	207	7	214	97
	tree	4	13	17	78
	Total	211	20	231
	Producers (%)	98	64		Overall = 95

The overall accuracy of the classifier compared with manual interpretation was 90% or above for the three sites. The classifier underestimates the area of tree as compared with the human operator in each of the three sites.

Table 5. Tree accuracy for the year 2009.

		Manual interpretation
Class label		Non-tree	Tree	Total	Users (%)
Site 1	Non-tree	190	23	213	89
	Tree	0	47	47	100
	Total	190	70	260
	Producers (%)	100	67		Overall = 91
Site 2	Non-tree	760	80	840	90
	Tree	1	87	88	99
	Total	761	167	928
	Producers (%)	100	52		Overall = 91
Site 3	Non-tree	212	4	216	98
	Tree	3	12	15	80
	Total	215	16	231
	Producers (%)	99	75		Overall = 92

The overall accuracy of the classifier compared with manual interpretation greater than 90% for the three sites. The classifier underestimates the area of tree as compared with the human operator in each of the three sites.

Figure 5. Area of trees [log₁₀(Area_Trees_km²)] by height (m) for the years 2007 and 2009. The estimates show no major departure across the height range.

Table 6. Vegetation summary statistics for the region for the years 2007 and 2009.

	Vegetation summary
	2007 sq. km. (and % of area captured)	2009 sq. km. (and % of area captured)
Area captured	9396 (100)	9303 (100)
Area of vegetation	3219 (34.2)	2583 (27.7)
Area of vegetation above 10 m	413 (4.4)	400 (4.3)
Area of vegetation between 2 and 10 m	884 (9.4)	851 (9.1)
Area of vegetation between 0.5 and 2 m	464 (4.9)	394 (4.2)
Area of vegetation below 0.5 m	1494 (15.9)	937 (10.1)
Height distribution of vegetation of height 2 m or more
Mean height of vegetation above 2 m	8.23 m	8.25 m
Standard deviation of vegetation above 2 m	5.12 m	5.07 m

Table 7. Tree canopy and height summary by local government area for the years 2007.

	Year 2007 tree area and height
	Area km^2		Tree height
Locality	Estimate	%	Mean	Std	Total non-null area km^2
MANDURAH, CITY OF	27.69	14.28	6.71	8.01	193.88
WANNEROO, CITY OF	112.82	16.26	9.37	10.93	693.67
COCKBURN, CITY OF	16.68	9.66	5.98	7.09	172.69
JOONDALUP, CITY OF	10.50	10.16	6.22	7.48	103.34
EAST FREMANTLE, TOWN OF	0.42	11.77	6.21	7.06	3.57
FREMANTLE, CITY OF	1.81	9.32	6.35	7.43	19.38
CLAREMONT, TOWN OF	1.04	20.85	7.33	8.57	4.96
COTTESLOE, TOWN OF	0.55	14.05	6.11	7.09	3.91
CAMBRIDGE, TOWN OF	4.37	19.86	7.16	8.51	22.01
VINCENT, CITY OF	1.49	13.08	6.97	8.34	11.38
SUBIACO, CITY OF	1.47	21.13	7.99	9.30	6.97
PEPPERMINT GROVE, SHIRE OF	0.29	27.55	7.39	8.48	1.06
STIRLING, CITY OF	12.64	12.06	6.65	7.87	104.76
VICTORIA PARK, TOWN OF	2.27	12.75	7.97	9.52	17.82
BASSENDEAN, TOWN OF	1.63	15.79	7.04	8.27	10.31
MOSMAN PARK, TOWN OF	0.67	15.60	6.42	7.47	4.31
NEDLANDS, CITY OF	4.58	23.02	6.97	8.18	19.89
BAYSWATER, CITY OF	3.80	11.63	6.69	7.88	32.65
SOUTH PERTH, CITY OF	3.21	16.35	7.19	8.61	19.63
MELVILLE, CITY OF	7.41	14.07	6.61	7.88	52.66
CANNING, CITY OF	6.76	10.46	6.50	7.64	64.58
BELMONT, CITY OF	3.47	8.82	6.78	7.89	39.36
GOSNELLS, CITY OF	17.66	13.92	7.09	8.28	126.87
KWINANA, TOWN OF	15.92	13.32	6.62	8.00	119.48
ROCKINGHAM, CITY OF	28.71	11.30	7.41	9.08	254.12
PERTH, CITY OF	0.86	10.76	8.78	10.52	7.95
*SWAN, CITY OF	146.54	14.90	8.12	9.49	983.51
*KALAMUNDA, SHIRE OF	69.49	30.99	8.81	10.13	224.23
*MUNDARING, SHIRE OF	106.08	21.53	8.46	9.86	492.58
*ARMADALE, CITY OF	81.00	21.45	8.75	10.17	377.59
*SERPENTINE-JARRAHDALE, SHIRE OF	135.69	18.98	8.68	10.20	714.73
*WAROONA, SHIRE OF	79.36	14.86	9.09	10.73	534.10
*CHITTERING, SHIRE OF	80.35	9.97	7.04	8.06	805.60
*MURRAY, SHIRE OF	85.61	8.68	7.74	9.00	986.79
*HARVEY, SHIRE OF	105.18	16.68	9.62	11.19	630.43
*NORTHAM, SHIRE OF	3.44	9.74	7.22	8.25	35.28
*TOODYAY, SHIRE OF	7.45	13.09	6.82	7.95	56.91
*WANDERING, SHIRE OF	8.78	15.02	8.05	9.51	58.50
*GINGIN, SHIRE OF	98.51	8.48	7.41	8.89	1161.15

*Entries correspond to incomplete spatial coverage for the shire.

Table 8. Tree canopy and height summary by local government area for the year 2009.

	Year 2009 tree area and height
	Area km^2		Tree height
Locality	Estimate	%	Mean	Std	Total non-null area km^2
MANDURAH, CITY OF	25.41	12.83	6.80	8.04	198.06
WANNEROO, CITY OF	64.77	9.35	8.21	9.89	692.53
COCKBURN, CITY OF	18.25	10.65	6.15	7.28	171.42
JOONDALUP, CITY OF	10.91	10.65	6.26	7.54	102.44
EAST FREMANTLE, TOWN OF	0.50	14.07	6.19	7.04	3.56
FREMANTLE, CITY OF	1.90	9.81	6.32	7.38	19.33
CLAREMONT, TOWN OF	0.90	18.19	7.57	8.82	4.96
COTTESLOE, TOWN OF	0.54	13.72	6.14	7.14	3.92
CAMBRIDGE, TOWN OF	3.69	16.79	7.31	8.65	21.97
VINCENT, CITY OF	1.45	12.73	7.05	8.43	11.37
SUBIACO, CITY OF	1.33	19.09	8.10	9.39	6.96
PEPPERMINT GROVE, SHIRE OF	0.24	22.17	7.61	8.74	1.06
STIRLING, CITY OF	12.29	11.74	6.62	7.84	104.67
VICTORIA PARK, TOWN OF	2.23	12.49	7.59	9.06	17.83
BASSENDEAN, TOWN OF	1.47	14.23	7.21	8.44	10.32
MOSMAN PARK, TOWN OF	0.67	15.55	6.42	7.47	4.31
NEDLANDS, CITY OF	3.54	17.80	7.39	8.64	19.89
BAYSWATER, CITY OF	3.63	11.27	6.55	7.73	32.20
SOUTH PERTH, CITY OF	2.85	14.52	7.45	8.87	19.63
MELVILLE, CITY OF	7.22	13.70	6.74	8.02	52.66
CANNING, CITY OF	6.56	10.15	6.50	7.70	64.67
BELMONT, CITY OF	3.45	8.75	6.60	7.71	39.39
GOSNELLS, CITY OF	19.13	15.06	7.24	8.44	126.96
KWINANA, TOWN OF	17.07	14.28	6.99	8.45	119.53
ROCKINGHAM, CITY OF	27.68	10.79	7.64	9.26	256.42
PERTH, CITY OF	0.73	9.17	8.75	10.19	7.94
*SWAN, CITY OF	126.22	12.83	8.00	9.26	984.13
*KALAMUNDA, SHIRE OF	62.85	28.03	8.91	10.26	224.21
*MUNDARING, SHIRE OF	94.18	19.03	8.48	9.89	494.86
*ARMADALE, CITY OF	101.50	26.80	8.60	10.01	378.67
*SERPENTINE-JARRAHDALE, SHIRE OF	146.73	20.46	8.63	10.08	717.02
*WAROONA, SHIRE OF	89.99	16.83	9.33	10.87	534.57
*CHITTERING, SHIRE OF	72.66	8.99	7.27	8.23	808.55
*MURRAY, SHIRE OF	107.83	10.95	8.48	9.77	985.11
*HARVEY, SHIRE OF	103.25	16.25	9.95	11.47	635.26
*NORTHAM, SHIRE OF	4.64	13.06	7.84	8.83	35.50
*TOODYAY, SHIRE OF	7.64	13.26	6.96	7.86	57.60
*WANDERING, SHIRE OF	12.90	22.05	7.85	9.42	58.49
*GINGIN, SHIRE OF	81.43	7.00	7.10	8.60	1163.23

*Entries correspond to incomplete spatial coverage for the shire.

Collings, S., P. A. Caccetta, N. A. Campbell, and X. Wu. 2011. “Empirical Models for Radiometric Calibration of Digital Aerial Frame Mosaics.” IEEE Transactions on Geoscience and Remote Sensing 49 (7): 2573–2588. doi:10.1109/TGRS.2011.2108301

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