no we can not say that, solar pond is consist of brine solution (salt water) and it can be divide in three layers on the basis of gradient of concentration of salt.

The top layer, which has a low salt concentration.

An intermediate insulating layer with a salt gradient, which establishes a density gradient that prevents heat exchange by natural convection.

The bottom layer, which has a high salt content and high density .

So first you must know its molar solution , depth of each layer and heat transfer coefficient for that given layer

Then how can we find out its absorptivity, fraction of incident solar Insolation absorbed by the pond?

You can either do a colorimetric test of the pond (measure the temperature variation of the pong under radiation heating and assume the energy absorbed equals the variation in internal thermal energy of the pond), or measure the reflected radiation by the pond. If the pond is deep enough, it is likely no radiation will be transmitted through it, in which case the measuring of the reflected radiation will suffice (otherwise you would have to find out how much of the incident radiation is transmitted through the pond as well). Neither of these alternatives are easy to implement in a pond, but they are relatively easy to do in a laboratory setting.

Though there is fresh water in top layer, effective absorptivity of Solar pond would be greater than fresh water. Measuring it accurately may not be possible, but its effectiveness can be accounted indirectly by measuring the amount of energy extracted from solar pond (with diff salt concentrations) and fresh water pond.

the research paper shows detail information about the solar pond operation.