  We have developed a new method to correct dark current at relatively high
temperatures for Charge-Coupled Device (CCD) images when dark frames cannot be
obtained on the telescope. For images taken with the Antarctic Survey
Telescopes (AST3) in 2012, due to the low cooling efficiency, the median CCD
temperature was -46$^\circ$C, resulting in a high dark current level of about
3$e^-$/pix/sec, even comparable to the sky brightness (10$e^-$/pix/sec). If not
corrected, the nonuniformity of the dark current could even overweight the
photon noise of the sky background. However, dark frames could not be obtained
during the observing season because the camera was operated in frame-transfer
mode without a shutter, and the telescope was unattended in winter. Here we
present an alternative, but simple and effective method to derive the dark
current frame from the scientific images. Then we can scale this dark frame to
the temperature at which the scientific images were taken, and apply the dark
frame corrections to the scientific images. We have applied this method to the
AST3 data, and demonstrated that it can reduce the noise to a level roughly as
low as the photon noise of the sky brightness, solving the high noise problem
and improving the photometric precision. This method will also be helpful for
other projects that suffer from similar issues.
