River delta / saline intrusion

Benefits

• Sentinel-2 spatial and temporal resolutions is suitable for monitoring saline intrusion of wide rivers (width at least > 10 m).

• A strong correlation was found between the reflectance from visible bands of the Sentinel-2 with river water salinity. This can be explained by the fact that when flowing freshwater mixes with sea water, flocculation and settling of suspended particles are induced, resulting in less turbidity as the salinity increases.

Limitations

• The method based on Sentinel-2 imagery cannot be applied to small rivers (width < 10 m).

• Field measurements used for calibration have to be collected the same day than the image to be representative (low-flow conditions had less fluctuations).

• Cloud-cover limits the image availability.

Applicability for Northland

Yes, likely for wide rivers.

Finer spatial scale imagery would allow to cover smaller rivers. In situ-measurements and calibration would be required to confirm applicability.

Techniques applying optical data will be limited in coverage and temporal granularity by the persistent cloud cover in the region, particularly during the winter months. Mature cloud-masking techniques are directly available for open access multispectral data (e.g. Landsat and Sentinel-2). When using commercial data, care must be taken to ensure that there is sufficiently cloud free imagery available, as cloud masking is not as mature and ordering a large volume of imagery to ensure complete cloud free coverage between multiple observations can become cost prohibitive.