Constraining the local reddening distribution of SA 98 by star counts

We present B, V, and I photometry of the stellar field SA 98 in the plane of the Galaxy. This field is located on the opposite side of the Galactic center, in the direction of the Monoceros region. The magnitude and color counts predicted by & van Altena's Galactic structure and reddening model, Mendez based on the reddening maps derived from the work of FitzGerald and Neckel & Klare or on Schlegel, Finkbeiner, & Davis's total reddening values, do not agree with the observations. Detailed inspection by means of color-color diagrams of selected Landolt standard stars within SA 98 shows a strong clumpiness and inhomogeneity of the reddening distribution along the line of sight. These color-color diagrams allow an optimization of the model-predicted color counts. A disk scale length of about 2.0 kpc based on the color counts of giant stars seems to be favored. Our findings also provide evidence to suggest that a supplemental reddening-heliocentric distance relation other than a simple exponential function must be used to apply the Schlegel et al. values at low Galactic latitude to construct reddening maps.