Category: Methods

I ordered a Delta-T BF5 sensor. This sensor measures PAR, but with a twist. It measures separately direct and diffuse radiation. It should arrive in approximately 3 weeks time.

See the description in Delta-T’s web pages for more information.

The Maya Pro has had the optical bench realigned to optimize performance in UV-B region of the spectrum. Also the aperture has been replaced with a new smaller custom aperture. From the figures sent by the Ocean Optics people, performance seems to have been improved significantly. Our Maya Pro is on its way to Helsinki. Of course, Lasse Ylianttila will have to recalibrate it before it can be used.

We fetched the Maya from STUK two days ago. Performance for measuring effective UV doses is not as good as we had expected. We may have to send it back to Ocean Optics for checking… It is usable for doses if one is very careful, and very good for measuring unweighted UV and visible spectral irradiances. It should be very good for its main intended use, measuring spectral irradiance in plant canopies.

Our new Maya 2000 Pro is back at Lasse Ylianttila’s lab for calibration with the new Bentham D7-H-SMA cosine diffuser. We will get it back soon. We have been in touch with Ocean Optics about the bad stray light performance. They think that one reason for this is that our instrument has the HC-1 grating with a very wide spectral measuring range of 200 to 1100 nm. For our planned measurements we do need a range of at least 250 to 900 nm, but they think that UV-B performance would have been better with a grating with the upper limit at 650 nm. The problem can be overcome by measuring the stray light using an UV blocking filter, but this adds one more step to each measurement. As we do need to measure both UV and visible radiation probably there would not be any better instrument available, at least from Ocean Optics, for doing our measurements. However, for measuring UV-B alone this is not the handiest instrument.

We expect to start using the Maya in a few weeks time to measure sunlight outdoors and in greenhouses, and later on within plant canopies. Measuring spectra and temporal variation of light quality within canopies could be an interesting MSc thesis project. Please, contact me if you are interested.

Lasse Ylianttila has now developed an stray light correction algorithm for our Ocean Optics Maya 2000 Pro, and done the necessary calibrations and slit function measurements with different lasers. Developing an stray light correction for the Maya was more complex as, unexpectedly, this top-of-the-range model behaved worse with respect to stray light than the cheaper and older Ocean Optics S2000. We are still waiting for the Bentham cosine diffuser to be delivered, but meanwhile Lasse has lent us an Ocean Optics diffusser. The spectral irradiance calibration will need to be repeated when we get our own diffuser.