Camtracker: a new camera controlled high precision solar tracker system for FTIR-spectrometers

Abstract

Abstract.A new system to very precisely couple radiation of a moving source into a Fourier Transform Infrared (FTIR) Spectrometer is presented. The Camtracker consists of a homemade altazimuthal solar tracker, a digital camera and a homemade program to process the camera data and to control the motion of the tracker. The key idea is to evaluate the image of the radiation source on the entrance field stop of the spectrometer. We prove that the system reaches tracking accuracies of about 10 arc s for a ground-based solar absorption FTIR spectrometer, which is significantly better than current solar trackers. Moreover, due to the incorporation of a camera, the new system allows to document residual pointing errors and to point onto the solar disk center even in case of variable intensity distributions across the source due to cirrus or haze.

Accomplishments of the MUSICA project to provide accurate, long-term, global and high-resolution observations of tropospheric {H<sub>2</sub>O,<i>δ</i>D} pairs – a review

“…There, humidity is much more variable and the moisture pathways can be best investigated by analysing the distribution of the {H 2 O,δD} pairs (e.g. Galewsky et al, 2005;Noone, 2012;González et al, 2016). Recently, there have been a variety of publications that use remote sensing observations of tropospheric {H 2 O,δD} pairs for tropospheric moisture pathway studies: for instance, for estimating the importance of rain recycling (e.g.…”

Development of a digital mobile solar tracker

“…An overall loop rate of 15-20 Hz is realized. Camera-based feedback loops without access to the Euler coordinates have previously been used to precisely track the sun from a stationary setup (Gisi et al, 2011) and a research vessel (Bertleff, 2014).…”

“…However, the angular diameter of the solar disk is 0.53 • in the sky, and the motion compensation system by itself is not good enough to track the sun accurately while moving. The imaging setup is needed for very high tracking precision and has previously been described in a ground-based stationary system (Gisi et al, 2011) and a research vessel (Bertleff, 2014). However, we have found that with the uneven motion on the road, the imaging setup alone cannot track the sun continuously during drives at any reasonable angular precision and duty cycle.…”

“…This calculated sun position in the local vehicular coordinate system provides the coarse mirror angles to the motors to bring the solar disk into the FOV of the camera. The solar disk images are recorded and evaluated to determine the center position of the aperture and the solar disk (Gisi et al, 2011). First, a threshold is applied to convert the image to binary format to distinguish the bright solar disk from the dark aperture plate and aperture.…”

An automated method for the evaluation of the pointing accuracy of Sun-tracking devices

“…In fact, the determination of pointing accuracy is a common challenge for most types of Sun-pointing instruments, and various approaches have been presented to address this issue. For example, innovative camera-based (e.g., Gisi et al, 2011) and camera-free (e.g., Reichert et al, 2015) approaches to monitor tracking accuracy have been presented in the field of solar Fourier transform infrared (FTIR) spectrometry. While Gisi et al (2011) documents a camera setup with real-time image-evaluation and tracking software (CamTrack), Reichert et al (2015) presents an approach based on subsequent FTIR measurements with a different orientation of the solar rotation axis relative to the zenith direction, which allows us to obtain both mispointing components, the component in the zenith direction, and the component perpendicular to the solar rotation axis.…”