New challenges in New Zealand

After Fiji, we headed on to Christchurch, New Zealand with the ATom mission. Since we want to get good global coverage on ATom, and see the most remote parts of the atmosphere, we headed as far south of New Zealand as fuel would allow, before returning north to land. We passed the remote, but inhabited Chatham Island and even smaller, uninhabited Pitt and Pyramid islands. This far south winds are often very high and the ocean gets very choppy. A few of the dips we made as we headed south showed an uncharacteristically calm ocean, then we went up high before the last dip, and descended through cloud to find the situation had changed dramatically. The video below is taken from 1000ft above the ocean, the lowest level we can fly with the DC-8.

Before landing in Christchurch we tried to do an overpass at Lauder, where there are ground-based measurements we could compare with. But the combination of low cloud and high mountains made it too dangerous to go low enough and, after a few tries we had to give up.

The optics I had fixed on my instrument in Fiji looked good throughout the 10h flight to New Zealand, but the channel next to it started showing false counts and was intermittently problematic throughout the flight. While the problem was pretty small, about 10% of the time in 1 out of 10 channels, I wanted to fix it if I could.

Chatham Island seen from the DC-8
 Working on the plane in Christchurch in what is early spring there was a high contrast to working in Fiji. I layered up in a fleece and coat and was still chilly. At first I thought the problem might be the same as I’d seen with the neighboring channel in Fiji – a misaligned beam block – but a close examination of the signal showed no wandering baseline. I found I could induce the over-counting by pressing on the optics block, or putting a small torque on it. The lead me to believe I had a bad electrical connection on the board that controls the optics, but after some searching this proved not to be the case. In the end, the answer was deceptively simple: the board was not screwed quite tightly enough onto the optics block and could rotate slightly if shaken or pushed. Since the laser is attached to this board, this pulls it slightly out of alignment – leading to over-counting as some of the beam goes around the block. I screwed it on tighter and the problem was solved!

It bothered me that two problems could show up so close in time to each other, and be unrelated. I kept thinking about it, as it was unlikely to be just a coincidence. Later that evening I realized that probably that board has always been a bit loose, but I must have knocked it slightly out of position in Fiji while working on the neighboring channel. This put it close enough to the edge that in-flight vibrations could move it in and out of alignment, causing the intermittent problems I’d seen.

Coastal views on a hike near Christchurch, New Zealand

We has two days in Christchurch, so after working on the plane the first day, and analyzing data the second morning, I had some free time to meet up with and old friend who lives there. He took me on a lovely coastal walk called “Taylor’s Mistake”, just outside of the city. My luck was in, as the rain, which had been pretty incessant since we landed, stopped just as we started our walk, and then sun even poked through the clouds. It was stunningly beautiful, and I was completely charmed by the abundance of new lambs roaming the hillside.

The next morning, we started a very cold pre-flight at 4am, and took off for Punta Arenas at the very southern tip of Chile.

Sheep and lambs neat Lyttelton, Canterbury, New Zealand