Laboratory measurements of the spectral properties of estuarine suspended particles

Abstract

Laboratory measurements have been made of the spectral reflectance of size-fractionated suspended sediments from two estuarine systems. The results show that reflectance at wavelengths between 400 and 1000 nm increases with decreasing particle size for given sediment masses. Preliminary interpretation suggests that a new factor, target area, which is derived from the volume and number distribution of particles in a suspension, is proportional to the reflectance of the suspension. Reflectance in the near infra-red is shown to be unaffected by other in-water parameters and is also largely independent of the colour or nature of the particles. The relationship between spectral reflectance in the near infra-red and target area therefore provides a means of estimating suspended sediment concentration from remotely sensed imagery if the particle size distribution is known or can be estimated.

Remote Sensing of Particle Cross-Sectional Area in the Bohai Sea and Yellow Sea: Algorithm Development and Application Implications

“…Theoretical, experimental and in situ studies have proved that the inherent optical properties of suspended particles are more sensitive to AC than TSM [6,11,12,15] because of the direct dependences of the chance of a photon interacting with a particle on cross-sectional area rather than mass [7]. Consequently, remote sensing reflectance R rs (λ) as a function of light absorption and backscattering is also more strongly related to AC than TSM [7,8,18]. In this study, as expected, our analysis showed that although the AC varied over a large range, the correlations between AC and R rs (λ) at six bands of GOCI were strong and were approximately 1.4 times higher than those between R rs (λ) and TSM (Figure 4).…”

“…This may cause an unstable relationship between TSM and R rs (λ), and thereby bring large errors in TSM estimations which could reach a factor of 10 if their values are derived from satellite measurements [8,18,58]. The reason for the large uncertainties is attributed to the fact that R rs (λ) reflects the information not only for TSM but also for particle size distribution and density which might also vary by up to several orders of magnitude from location to location due to changes in particle composition and flocculation [13,59].…”

“…For AC, several studies have also examined its relationship with remote sensing reflectance (R rs (λ)), and compared with that between R rs (λ) and TSM [7,8,14,18]. For instance, during a laboratory experiment, Bale et al [18] observed that when the size of the suspended particles varied from large to fine, R rs (λ) increased 10-fold despite the constant value of TSM, while such increases in R rs (λ) were strongly correlated with AC, showing a R 2 value of 0.897. Meanwhile, based on field observations, Mikkelsen [8] showed that reflectance spectra are highly dependent on AC rather than TSM.…”

A method for estimating inherent optical properties of New Zealand continental shelf waters from satellite ocean colour measurements

“…a concentration, and non-algal particle ("sediment") concentration. An important advantage of such IOP algorithms is that the relationship between remote sensing reflectance and the IOPs of the water column is largely independent of the type of material in the water (e.g., Bale et al 1994). Therefore, this first part of the algorithm may be applicable to many regions around the world without major tuning of the method.…”

“…Relationships between IOPs and biogeochemical variables are often highly variable between different bio-optical provinces, depending on the nature of inorganic sediment (particle size distribution, particle shape, particle mineralogy, etc. ), and the local phytoplankton species composition (e.g., Bale et al 1994;Bricaud et al 1995;Babin et al 2003a,b). This paper concerns the first part of an IOP-centred approach to ocean colour data processing only.…”