  Comet Hale-Bopp was observed five times with ISOPHOT, the photometer on board
the Infrared Space Observatory (ISO). Each time broadband photometry was
performed using 4 different detectors, 5 apertures and, 10 filters covering the
range between 3.6 to 175 $\mu$m. Calibration measurements using the internal
Fine Calibration Source were done together with each individual measurement.
Background observations were performed with identical instrument settings at
the same positions on the sky several days after the comet observations. The
observation strategy and the initial data reduction steps are described in some
detail and the resulting in-band power values of the Hale-Bopp observations and
their uncertainties are derived. Initial reduction of these measurements was
performed in 3 steps: (1) processing of raw data by removing instrumental and
energetic particle effects, (2) averaging of the individual signals, and (3)
determination of the detector responsivities and their uncertainties. The
detector signal is determined by two different methods and the best value is
chosen. At the present level of processing uncertainties range from 10% to a
factor of 3 for the low power levels at short wavelengths. The in-band power
levels at different wavelengths varied over 3 orders of magnitude.
