Effective remote sensing DIAL transmitters require accurate and rapid monitoring of their wavelength and spectral linewidth. For mid-wave and long-wave IR transmitters, an absolute measurement resolution on the order of 0.1 cm-1 allows for accurate turning of the source onto narrow absorption lines of atmospheric molecules. Unfortunately, pulsed wavemeters with this level of resolution, that also operate outside of the visible and near IR regions, are not readily available. We have, therefore, designed and constructed a suitable spectral diagnostic instrument for use with an optical parametric oscillator-based DIAL transmitter. The transmitter is capable of emitting simultaneously in the 3-4 micron and 8- 13 micron regions. Although the operating wavelength range of the wavemeter is restricted to 1.4-1.85 microns, relationships between pump, signal and idler wavelengths, along with a nonlinear frequency mixing technique, allow the wavemeter to serve as a complete spectral diagnostic for this broadband transmitter. The wavemeter architecture is based on a combination grating spectrograph and single-stage Fabry-Perot etalon design.