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We present the $^{13}$CO/C$^{18}$O (J=3-2) Heterodyne Inner Milky Way PlaneSurvey (CHIMPS) which has been carried out using the Heterodyne Array ReceiverProgram on the 15 m James Clerk Maxwell Telescope (JCMT) in Hawaii. Thehigh-resolution spectral survey currently covers |b| < 0.5 deg and 28 < l < 46deg, with an angular resolution of 15 arcsec in 0.5 km/s velocity channels. Thespectra have a median rms of $\sim$ 0.6 K at this resolution, and for opticallythin gas at an excitation temperature of 10 K, this sensitivity corresponds tocolumn densities of $N_{\mathrm{H}_{2}} \sim 3 \times 10^{20}\,$cm$^{-2}$ and$N_{\mathrm{H}_{2}} \sim 4 \times 10^{21}\,$cm$^{-2}$ for $^{13}$CO andC$^{18}$O, respectively. The molecular gas that CHIMPS traces is at highercolumn densities and is also more optically thin than in other publiclyavailable CO surveys due to its rarer isotopologues, and thus morerepresentative of the three-dimensional structure of the clouds. The criticaldensity of the J=3-2 transition of CO is $\gtrsim 10^{4}$ cm$^{-3}$ attemperatures of $\leq 20$ K, and so the higher density gas associated with starformation is well traced. These data complement other existing Galactic planesurveys, especially the JCMT Galactic Plane Survey which has similar spatialresolution and column density sensitivity, and the Herschel infrared GalacticPlane Survey. In this paper, we discuss the observations, data reduction andcharacteristics of the survey, presenting integrated emission maps for theregion covered. Position-velocity diagrams allow comparison with Galacticstructure models of the Milky Way, and while we find good agreement with aparticular four arm model, there are some significant deviations.

CHIMPS: the $^{13}$CO/C$^{18}$O (J=3-2) Heterodyne Inner Milky Way Plane Survey