Best Practices for Field Spectroscopy
Intention of Best Practice Discussion
All spectrometers loaned by the facility are provided alongside one-to-one training for the loan user. This training is tailored to the science and methodology of the loan application, and the advice provided will be unique between loans. However, the following provides a standard checklist of best practices for bi-conical field spectroscopy, which covers the majority of applications covered by the facility.
Before Heading to your Field Site
- Make sure that your field spectrometer batteries are fully charged – you will usually receive between 2 to 4 batteries with a spectrometer supplied by the facility. Depending on the type of measurements you are taking, battery lifetime may range from 3 hours to as low as 1 hour. Make sure that you have planned accordingly, and have fully charged all the batteries you intend to bring to your site.
- Ensure that all items have been tested before going into the field. This not only includes the spectrometer, but also important peripherals, such as the controlling PC, laptop or tablet, or the field spectrometer accessories, such as leaf clips, integrating spheres, or lamps.
- Clothing – do not wear clothing which could reflect light, like high-vis or white shirts. This can affect your measurements significantly.
- Field spectroscopy can be conducted by a single individual, but for best measurements – as well as ensuring checks on field spectrometer orientation and enabling good logs – try to enlist the help of others.
During measurements
- Switch on the spectrometer for at least 10 to 15 minutes before measurements begin. This is especially important for cooled detector units, like the extended SWIR sensors of field spectrometers, or the OP-FTIR.
- Know your instrument’s field of view, and how that translates to sampling area. You want to capture as much of your sample as possible, but not to include other material. Sampling area is linked to your foreoptic FoV. Utilize the field of view calculator to determine the correct foreoptic to use, and what height to keep the spectrometer from the target.
- To reduce the azimuth and zenith angular effects on measurements, keep your spectrometer and/or reference panels level.
- Be aware of light conditions –- you want to aim for noon measurements to reduce the impact of solar zenith on your reference measurements. Get into the habit of taking frequent white reference measurements (a 1 white reference to 2 target measurements strategy is ideal, always take a new white reference measurement if light levels change.)
- On the effects of clouds:
- Cirrus clouds are difficult to spot but can significantly alter absolute intensity and spectral shape. Bringing sunglasses can help to safely identify high level clouds close to the Sun.
- Partial cloud cover also contributes significantly to diffuse skylight illumination.
- You should seek to minimise the time between target and reference measurements.
- Maintain good logs – taking detailed metadata significantly improves the quality of your data. Location, weather, and ancillary information (such as the species of the object measured, or the physical state of the object) are all important qualities to note.