Unmanned aerial vehicles (UAVs) equipped with optical sensors facilitate non-invasive, real-time vegetation analysis. To guarantee robust scientific analysis, protocols need to be developed and sensors must be compared to state-of-the-art instruments. Here we compare four UAV sensors (RGB, NIR, six-band, spectrometer) to evaluate their applicability for vegetation monitoring. By showing the opportunities and pitfalls of UAV-based sensing, we describe ways to gather sound scientific data.