Towards developing comparable optical and SAR remote sensing inundation mapping with hydrodynamic modelling

Figures & data

Table 1. Characteristics of sensors used in this analysis. ‘Spatial resolution’ contains the value used in this analysis (some sensors have a range of spatial resolutions).

Sensor	Spatial resolution	Operating time	Frequency
Landsat	30 m	1987 to present	8–16 days
MODIS	500 m	2000 to present	Daily
Sentinel-2	20 m	2016 to present	5–10 days
VIIRS	350 m	2011 to present	Daily
Sentinel-1	20 m	2015 to present	6–12 days
NovaSAR-1	20 m	2019 to present	tasked

Figure 1. Study area map showing major rivers, stream gauge and land subject to inundation.

Table 2. Characteristics of the recent flood events in the Fitzroy floodplain (ARI = annual recurrence interval).

Start Date	End Date	Duration (days)	Maximum Flow (m^3/s)	Maximum Flow Date	ARI
15/02/2001	14/03/2001	28	6080.83	21/02/2001	10
20/02/2002	7/03/2002	16	15456.89	24/02/2002	25
25/02/2011	29/03/2011	33	14138.57	16/03/2011	24
8/02/2017	22/02/2017	15	6662.36	17/02/2017	16
3/03/2020	8/03/2020	6	5076.32	4/03/2020	5

Table 3. Number of scenes available from each sensor for each flood event.

Start date	End Date	Landsat	MODIS	Sentinel-2	Sentinel-1	NovaSAR-1	VIIRS
15/02/2001	14/03/2001	2	11
20/02/2002	7/03/2002		8
25/02/2011	29/03/2011	1	8
8/02/2017	23/02/2017	2	5	1	2		6
3/03/2020	11/03/2020	1	6	3	2	1	8

Figure 2. Spatial comparison of Landsat (LS), MODIS (MD), Sentinel-1 (S1), NovaSAR-1 (N1), Sentinel-2 (S2) and VIIRS (VI) with the hydrodynamic (HD) model water extent for different flood dates (F1 score is shown in brackets next to date, RS = remote sensing data).

Table 4. Summary results for remote sensing data compared to hydrodynamic model.

Sensor	Number of images	Mean PA	Mean UA	Mean F1	Min F1	Max F1
Landsat	6	0.59	0.76	0.65	0.26	0.83
MODIS	38	0.51	0.87	0.61	0.17	0.92
Sentinel-2	4	0.58	0.58	0.57	0.23	0.72
VIIRS	14	0.51	0.68	0.58	0.33	0.73
NovaSAR-1	1	0.22	0.77	0.35	0.35	0.35
Sentinel-1	4	0.20	0.69	0.31	0.19	0.38

Figure 3. Spatial comparison of proportion of agreement (‘HD water, RS water’) and disagreement (‘HD water, RS dry’ and ‘RS water, HD dry’) for Landsat, MODIS, SAR (Sentinel-1 and NovaSAR-1), Sentinel-2 and VIIRS with the hydrodynamic model (HD) water extent as calculated from all common flood dates (RS = remote sensing data). The red dots show the location of Fitzroy Barrage (Figure 3g) and the junction of Fitzroy River and Christmas Creek (Figure 3l and Figure 3o).

Table 5. Summary results for remote sensing data compared to the hydrodynamic model for the dates close to flood peak (i.e. ±80% of flood peak).

Sensor	Number of images	Mean PA	Mean UA	Mean F1	Min F1	Max F1
Landsat	2	0.81	0.81	0.80	0.77	0.83
MODIS	13	0.62	0.82	0.70	0.53	0.92
Sentinel-2	2	0.77	0.68	0.72	0.72	0.72
VIIRS	8	0.55	0.69	0.61	0.51	0.73
NovaSAR-1	1	0.22	0.77	0.35	0.35	0.35
Sentinel-1	3	0.23	0.74	0.35	0.32	0.38

Figure 4. Spatial comparison of Landsat (LS), Sentinel-2 (S2), VIIRS (VI), Sentinel-1 (S1) and NovaSAR-1 (N1) with MODIS water extent for common flood dates (F1 score is shown in brackets next to date, RS = remote sensing data being compared to MODIS).

Figure 5. (a) Spatial comparison of Sentinel-2 and NovaSAR-1 water extent for 6^th March 2020. (b) Sentinel-2 image (RGB = Red, Green, SWIR-2 bands), (c) NovaSAR-1 water map, and (d) NovaSAR-1 VV image for subset area (black square).

Table 6. Summary results for remote sensing data compared to other coincident remote sensing data.

Sensors	Number of images	Mean PA	Mean UA	Mean F1	Min F1	Max F1
MODIS – Landsat	4	0.87	0.68	0.76	0.61	0.86
MODIS – VIIRS	10	0.81	0.80	0.80	0.75	0.83
MODIS – Sentinel-2	4	0.91	0.48	0.57	0.02	0.76
MODIS – Sentinel-1	4	0.24	0.75	0.36	0.32	0.43
MODIS – NovaSAR-1	2	0.38	0.60	0.46	0.46	0.46
VIIRS – Sentinel-2	1	0.87	0.47	0.56	0.08	0.75
VIIRS – Sentinel-1	3	0.22	0.67	0.34	0.28	0.41
VIIRS – NovaSAR-1	1	0.34	0.64	0.45	0.45	0.45
Sentinel-2 –NovaSAR-1	1	0.22	0.84	0.46	0.46	0.46

Figure 6. Spatial comparison of proportion of agreement (‘MOD water, RS water’) and disagreement (‘MOD water, RS dry’ and ‘RS water, MOD dry’) for Landsat, SAR (Sentinel-1 and NovaSAR-1), Sentinel-2 and VIIRS with the MODIS water extent as calculated from all common flood dates (RS = all remote sensing data except MODIS – which it is being compared to). The red dot shows the location of Noonkanbah in Figure 6a.

Data availability statement

The data that support the findings of this study are available from the corresponding author, CT, upon reasonable request.