# Characterisation of Coastal Sediment Properties from Spectral Reflectance Data
## 3 Results
### Spectral Analysis of Sediment Samples  
The spectral variation at the VNIR and SWIR bands can be examined in detail using the correlation matrices between selected sample particle size characteristics and CaCO\({}_{3}\) content. Here, we systematically calculate the correlation coefficient of D\({}_{10}\), CaCO\({}_{3}\), D\({}_{90}\), fine sand and kurtosis at 1 nm wavelength increments through the NVIR and SWIR wavebands (Figure 6). This shows that certain parts of the spectrum are associated with greater (positive or negative) correlation coefficient values and thus are more useful in terms of discriminating between different sediment properties at those wavelengths. For example, in the range \(\sim\)700-1350 nm there is a clear discrimination between high positive correlations for D\({}_{10}\) and D\({}_{90}\) and high negative correlation for fine sand (Figure 6). Here, kurtosis and CaCO\({}_{3}\) shows no correlation. Likewise, in the range \(\sim\)1850-2450 nm there is greater statistical discrimination between fine sand (highest positive correlation) and CaCO\({}_{3}\) (highest negative correlation) values. By contrast, the region \(\sim\)1450-1700 nm is not useful for discriminating any sediment properties, because there are very low correlation coefficients throughout (i.e., all correlation coefficients are around zero). The statistical relationships of CaCO\({}_{3}\) values, fine sand and grain size _span_ to different wavelengths are described in Table 4, which shows the outputs of a linear regression model for each variable. The results highlight that certain wavelengths have a statistically significant relationship to some sediment properties. For example, CaCO\({}_{3}\) shows greatest significance in the wavelength range \(\sim\)1052-1252 nm, which falls within the VNIR part of the spectrum. Fine sand has the greatest significance at shorter VNIR wavelengths (\(\sim\)852-952 nm), and _span_ shows significance in isolated parts of the spectrum (2300, 2400 and 2447 nm) at the end of the SWIR range, which may be an artefact of sediment composition within the sample as a whole, e.g., [47]. Water absorption at the 1352 nm waveband has a strong signal and therefore this waveband is removed from the analysis (Table 4) in order to avoid erroneous overfitting. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & \(D_{10}\) & \(D_{50}\) & \(D_{90}\) & **Kurtosis** & **Skewness** & **CaCO\({}_{3}\)** & **F Sand** & **M Sand** & **C Sand** & **VC Sand** \\ \hline \(D_{10}\) & 1.000 & & & & & & & & & \\ \hline \(D_{50}\) & 0.951 *** & 1.000 & & & & & & & & \\ \hline \(D_{90}\) & 0.754 *** & 0.903 *** & 1.000 *** & & & & & & & \\ \hline
**Kurtosis** & 0.139 & 0.318 *** & 0.634 *** & 1.000 & & & & & & \\ \hline
**Skewness** & \(-\)0.252 *** & \(-\)0.477 *** & \(-\)0.793 *** & \(-\)0.890 *** & 1.000 & & & & & \\ \hline
**CaCO\({}_{3}\)** & 0.571 *** & 0.679 *** & 0.698 *** & 0.337 *** & \(-\)0.463 *** & 1.000 & & & & \\ \hline
**F sand** & \(-\)0.914 *** & \(-\)0.918 *** & \(-\)0.761 *** & \(-\)0.156 * & 0.300 *** & \(-\)0.557 *** & 1.000 & & & \\ \hline
**M sand** & \(-\)0.201 * & \(-\)0.332 *** & \(-\)0.451 *** & \(-\)0.383 *** & 0.478 *** & \(-\)0.411 *** & 0.030 & 1.000 & & \\ \hline
**C sand** & 0.928 *** & 0.984 *** & 0.872 *** & 0.266 *** & \(-\)0.443 *** & 0.679 *** & \(-\)0.880 *** & \(-\)0.393 *** & 1.000 & & \\ \hline
**VC sand** & 0.414 *** & 0.603 *** & 0.853 *** & 0.813 *** & \(-\)0.895 *** & 0.566 *** & \(-\)0.367 *** & \(-\)0.529 *** & 0.545 *** & 1.000 \\ \hline
**Span** & 0.403 *** & 0.642 *** & 0.902 *** & 0.782 *** & \(-\)0.941 *** & 0.593 *** & \(-\)0.493 *** & \(-\)0.469 *** & 0.616 *** & 0.885 *** \\ \hline \end{tabular}
\end{table} 
Table 3: Pearson Product Moment Correlation of different sediment properties across all samples (\(n\) = 134). F = fine, M = medium, C = coarse and VC = very coarse. Variable _span_ is defined in the text. Significance levels are: * 0.1, * 0.05, ** 0.01 and *** 0.001.