  In this paper we present a novel method to estimate the time evolution of
proto-neutron star (PNS) structure from the neutrino signal in core-collapse
supernovae (CCSN). Employing recent results of multi-dimensional CCSN
simulations, we delve into a relation between total emitted neutrino energy
(TONE) and PNS mass/radius, and we find that they are strongly correlated with
each other. We fit the relation by simple polynomial functions connecting TONE
to PNS mass and radius as a function of time. By combining another fitting
function representing the correlation between TONE and cumulative number of
event at each neutrino observatory, PNS mass and radius can be retrieved from
purely observed neutrino data. We demonstrate retrievals of PNS mass and radius
from mock data of neutrino signal, and we assess the capability of our proposed
method. While underlining the limitations of the method, we also discuss the
importance of the joint analysis with gravitational wave signal. This would
reduce uncertainties of parameter estimations in our method, and may narrow
down the possible neutrino oscillation model. The proposed method is a very
easy and inexpensive computation, which will be useful in real data analysis of
CCSN neutrino signal.
