  The spatial coherence wavefront outer scale (L_0) characterizes the size of
the largest turbulence eddies in Earth's atmosphere, determining low spatial
frequency perturbations in the wavefront of the light captured by ground-based
telescopes. The motivation of this work is to introduce a novel technique for
estimating L_0 from seeing-limited integral field spectroscopic (IFS) data.
This approach is based on the impact of a finite L_0 on the light collected by
the pupil entrance of a ground-based telescope. We take advantage of the
homogeneity of IFS to generate band filter images spanning a wide wavelength
range, enabling the assessment of image quality (IQ) at the telescope's focal
plane. Comparing the measured wavelength-dependent IQ variation with
predictions from Tokovinin (2002) analytical approach offers valuable insights
into the prevailing L_0 parameter during the observations. We applied the
proposed technique to observations from MUSE in the Wide Field Mode obtained at
the Paranal Observatory. Our analysis successfully validates Tokovinin's
analytical expression, which combines the seeing (E_0) and the L_0 parameters,
to predict the IQ variations with the wavelength in ground-based astronomical
data. However, we observed some discrepancies between the measured and
predictions of the IQ that are analyzed in terms of uncertainties in the
estimated E_0 and dome-induced turbulence contributions. This work constitutes
the empirical validation of the analytical expression for estimating IQ at the
focal plane of ground-based telescopes under specific E_0 and finite L_0
conditions. Additionally, we provide a simple methodology to characterize the
L_0 and dome-seeing (E_d) as by-products of IFS observations routinely
conducted at major ground-based astronomical observatories.
