For an introduction to optical backscattering, I highly recommend the very easy-to-read "Why we should measure the optical backscattering coefficient" by Boss et al., 2003. (FYI, you'll find Emmanuel Boss here on ResearchGate.)

In theory, if there is a single type of scattering particle in the water, the backscattering coefficient (bb) is linearly proportional to the concentration of the scattering material. However, in real (esp. turbid) waters, this is likely not to be true. For example, see Wu et al. 2011 for an example of an observed non-linear relationship between total suspended matter (TSM / SPM) and backscattering.

Many other published relationships between optical quantities and total suspended matter (TSM / SPM) exist. See, for example, Babin et al. 2003 (scattering) and Bergman et al. 2004 (beam attenuation). So, you might want to investigate more than backscattering as your optical measurement.

In any case, you'll have to derive your own relationship between bb and TSM, as this relationship will vary based on the particle size distribution, refractive indices of the particles involved, absorption characteristics of the particles, and the instruments you are using. So, sample waters of interest, collect samples for TSM / SPM, and simultaneously measure bb. Then let us know what you find (publish!).

E. Boss, D. Stramski, T. Bergmann, W. Pegau, and M. Lewis, "Why should we measure the optical backscattering coefficient?," Oceanography 17, 44-49 (2004).

G. Wu, L. Cui, H. Duan, T. Fei, and Y. Liu, "Absorption and backscattering coefficients and their relations to water constituents of Poyang Lake, China," Appl. Opt. 50, 6358-6368 (2011).

M. Babin, A. Morel, V. Fournier-Sicre, F. Fell, and D. Stramski, "Light scattering properties of marine particles in coastal and open ocean waters as related to the particle mass concentration," Limnol. Oceanogr., 843-859 (2003).

T. Bergmann, G. Fahnenstiel, S. Lohrenz, D. Millie, and O. Schofield, "Impacts of a recurrent resuspension event and variable phytoplankton community composition on remote sensing reflectance," J. Geophys. Res. 109, C10S15 (2004).

Thank you for your valuable suggestion.

I have for some years observed the development of light-attenuation techniques for measurement of SPM (Suspended Particulate Matter). These are attractive, because one obtains a continuous record, sometimes in digital form, without the messy need to sample water.

Personally, I avoid these techniques. There is the constant need to calibrate against what is really there-and constraints of time and budget mean this corner is often cut.

I recommend measuring SPM directly, by the age-old technique of filtering water samples. This is slower, but has the trumps-everything advantage of producing an archived record of what was actually in the water. This allows one to seek out sources, data which may be (and have been) taken into a court of law.

It all depends on what you want to observe in particular. If you are interested in the mass of SPM, Michael Risk is right that in situ measurements are indispensable. Of you are interested in the optical (bulk) properties, you may want to dive more into the determination of the inherent and apparent optical properties of the suspended matter. In general I suggest to follow Eric Rehm's references first.

I gone through the papers suggested by Eric Rehm. I have also read others paper I found that if we know the back scattering coefficient then we may know the range of Suspended sediments but not exact quantitative values of SS.

You might like to read Davies-Colley & Smith (2001) which presents a review of turbidity,suspended sediment and water clarity and how they relate to each other:

Davies-Colley, R.J., Smith, D.G., 2001. Turbidity, suspended sediment, and water clarity: a review. Journal of the American Water Resources Association, 37(5), 1085-1101.

Thank you so much.

Hello Surya,

the thing is, depending on the composition of your particulates your relashionship between SS and backscattering will vary. I completely agree with Eric Rehm's suggestions up there and will add 2 cool papers to read:

Neukermans, Griet, et al. "Optimization and quality control of suspended particulate matter concentration measurement using turbidity measurements." Limnol. Oceanogr.: Methods 10 (2012): 1011-1023.

Neukermans, Griet, et al. "In situ variability of mass-specific beam attenuation and backscattering of marine particles with respect to particle size, density, and composition." Limnology and oceanography 57.1 (2012).

I

Thanks Ivona. I will read your suggested papers.

All these journal article suggestions are very pertinent to the question. The basic problem is that suspended sediment concentration is measured as mass per volume, while the particle size distribution (PSD) affects how efficiently that mass scatters light. Many of the suggested papers review this principle, though perhaps the Davies-Colley and Smith 2001 is one of the clearest presentations. An extreme example is that one gram of "rock" divided into clay particles (a few light wavelengths in diameter) will scatter light much more efficiently than a single one gram pebble. Thus the continuing efforts to develop workable approaches to comparing two methods that measure fundamentally different variables.

Good question. The estimation of the exact concentration of SPM is still very chalenging even trhough basic measurements based on water sampling. Optics will give you a rough proxy of SPM, but a high frequency and during long period of time. Among optical measurements you have to choose which one provides the less scatter in the optics vs. SPM relationship. According to the study performed in the frame of the PhD of Giret Neukermans (paper cites above) we showed that the backscattering coefficient is more suitable than the attenuation (i.e. scattering as it is in the red) to assess SPM concentration. The bbp/SPM ratio is much less vairable than the cp/SPM ratio. There is also a good paper by Emmanuel Boss et al. (2011) on that topics. Lisst measurements could also be used simultaneously to assess size, and with backscattering measurements, a rough proxy of refractive index can be estimated using the bbp/bp ratio (see paper by Mike twardovski et al. 2001in (JGR), or Loisel et al. (2007) in my list of publication). Note that ADCP measurements can also provide information on SPM, especially for large particles.

Your answer would help me to improve basic understanding on the backscattering due to suspended sediments. Thanks Dr. Loisel