  Unresolved sources of gravitational waves can create a stochastic
gravitational wave background (SGWB) which may have intrinsic or extrinsic
anisotropies. The angular power spectrum is a well-suited estimator for
characterizing diffuse anisotropic distributions in the sky. Here we estimate
the first model-independent all-sky all-frequency (ASAF) SGWB angular power
spectra in the 20-1726 Hz frequency range from the third observing run (O3) of
the Advanced LIGO and Advanced Virgo detectors. We develop a method to use the
spectrum's signal-to-noise ratio (SNR) as the detection statistic and show that
the distribution of the statistic obtained from the data agrees with the
analytical model. Since we find the data to be consistent with noise, $95\%$
confidence Bayesian upper limits are set on the angular power spectra, ranging
from $C_\ell^{1/2}\leq(3.1\times10^{-9}-0.76) \text{sr}^{-1}$. We also
introduce a method to combine the narrowband angular power spectra to obtain
estimators for broadband SGWB. These results can directly constrain theoretical
models which predict the SGWB angular power spectra and for estimating or
constraining the corresponding parameters. In addition, the results and the
techniques introduced in this work can be useful for performing
correlation-based searches, for instance, with electromagnetic observations.
