Return to the Northern FlightsAugust 30th, 2011 by Joanne Howl
Bangor, Maine 10:00 p.m. EDT
I’m Rafael Rincon, the principal investigator for DB-SAR, and I’m glad to tell you that things went very smoothly today. It was a good start to what should be a great week in the field.
I flew on the P3 last week and will be working this set of flights, too. I’ll be the one telling you about our work this week. Each day I’ll get up very early, spend the day in the air working the DBSAR, and once we are on the ground I analyze some data and help plan flights for the next day. After that is all done, I call our team writer, Joanne Howl, and give her the details of the day so she can get it written down and posted in the blog.
As you know, we had some challenges on our first week of flights. There were instrument problems, an earthquake, and a hurricane. The, once we began a really data collection run, we were cut off and had to land right away because of bad weather. Finally, they called the P3 home a day early, to protect it from what looked like it would be a direct hit from Hurricane Irene.
All I can say is this is the challenge of science in the field. You can expect the unexpected – it happens. And you just move ahead and work around it.
We’re set to have a great week. The aircraft is back home from West Virginia, where it was sheltered from Hurricane Irene. Our facility at Wallops is sound – no hurricane damage to be seen, and it is running well. The weather forecast for the next several days where we want to fly – Maine, Quebec and New Hampshire – is wonderful, with low winds and lots of sunshine. And our instruments are working fine. We have everything we need for a good trip.
What are the chances something will go wrong? Just as good as always! Just because we have a lot of challenges behind us, it doesn’t mean that there are no challenges ahead! It’s science, and we’re in the field. Things happen. We’ll take what comes and we’ll do our work, and we will overcome any problem that comes up.
This morning, there were no problems at all. We got up very early, and took off from Wallops at 9:00 a.m., just as planned. Flying north to Maine, we looked for evidence of hurricane damage, but we were flying so high we couldn’t see if trees were down on the ground – just too high for details. But there was one amazing thing that we could see.
When we were in transit from Wallops to Maine, at one point where the Hudson River comes into the ocean, we could see that the Hudson was very muddy from all the sediment washed into it from all the rain in Irene. And there was a big layer of mud that separated the coastline from the ocean water. It was thick mud, and it was huge – all along the shoreline, through the river and out into the ocean. It was very thick and we could see it very clearly. It was a very impressive sight.
When we arrived in Maine, we had some broken clouds, and this wasn’t the best for SIMPL or CAR. Those instruments can measure clouds, but for this mission we want them to look at canopy height of the forest. So if you get a cloud between the forest and those instruments, it reflects back to the aircraft, interfering with canopy measurements.
There were some areas of open sky, with no or few clouds, so Dave Harding, with SIMPL, decided to do his measurements first. We were flying low, at about 1200 meters (1.2 meters), which is the altitude that this instrument likes. We got a pretty good radar set for this lidar instrument, and breaks in the cloud let us get measurements of forest height with it.
After SIMPLE completed its measurements, it was the time for CAR to have its allocated turn. CAR is even more sensitive to clouds, so the PI, Charles Gatebe, decided not to use the time making those measurements now, but to wait for clearer skies tomorrow or Thursday to make those measurements.
After that, we went to a high altitude-about 5,500 meters (5.5 km) and I resumed the DBSAR measurements right where they were cut off last Thursday, when we were asked to land immediately due to weather.
We operate the radar in a couple of different modes. First we have a side looking synthetic aperture radar mode. The other is a wide beam mode. In wide beam we capture a full field of view under the aircraft. From there, we can synthesize as many beams as we want on either side of the aircraft. Each beam is basically a field of view of different spots on the ground, and we can look at specific spots because of the beam forming technique. So with wide beam we illuminate a wide view and by synthesizing the beam, we can look at a more narrow field.
This is a new technique and we tested before, and it worked well. This time we have added a test with a fully polarimetric measurement. We are doing that test for the first time ever, starting with this trip. And I can see that, so far, we are getting very good results.
How do I know the results are so good, already, since the data doesn’t get fully analyzed until we get back to the lab? I have two ways to tell. First, when we are collecting the data, I am watching the raw signal on my laptop. I see the display in real time, and I can see the shape and the extent of the signal as it comes in. This gives me a real good idea if the data is good or not.
Also, after the flight is over, then I download the data into my laptop and can generate a quick view for a few samples, so I can make sure the radar operated right away. For instance today I just processed a file we generated during the data collection today. It takes about a half-hour to process a quick look – I did that, and it looks very good. Each file holds about a gigabyte of data, and that’s for about 30 seconds of actual data collection. This quick processing will give us an image of an area of about 6 km in length and 4 km in width.
Just to make sure everything is working fine for the next flight. I pretty much do this each night.
I wanted to mention, also that we do collect data from the same area with each instrument, but we don’t usually operate them at the same time. We could do that if we wanted to do so, but ideal data collection conditions for DBSAR and SIMPL are different. The radar (DBSAR) likes to fly high – at about 5.5 kilometers. It is imaging a large surface area, so it needs to be up high to gather the data. The Lidar likes to fly low, at around 1.2 kilometers. It is low powered so if you go up too high, you can’t get the return form the ground.
There is an experimental mode in which we operate the radar as an altimeter, so we look at a single line straight on and can get the height of the forest. I have collected data with the radar and the lidar simultaneously in that mode. In that way, we can compare the two side by side, and it gives us additional information.
The weather tomorrow looks very good – winds are low with very little cloud cover expected. As soon as we take off, we’ll have SIMPL and CAR finish their measurements in Maine, and then we will head for Quebec, one of the other main sites for this campaign. It’s important, because the forest ecosystem type is different here. We are looking at a northern hardwood transitional forest here, with some boreal forest features, but the site in Quebec is a boreal forest. It’s important for us to get data from diverse ecosystems, so Quebec is important.
The one issue have right now is permission to turn on the lidar in Quebec. When you fly over a country’s sovereign territory, you can’t just go turn on instruments and fly around. You need government permissions to fly, and also permission to run each instrument. We requested, and had received, permission to turn the lidar on at our sites for last week. But it was over last week, and this week we do not have permission to work yet this week. We are waiting for an extension of the original permit, or a new one, and hope we get it by tomorrow’s flight. The radar (the DBSAR) has all authorizations granted, so we can fly the radar for sure. So we will fly, no matter what. It’s just a question of if we can gather data from SIMPL or not tomorrow. We hope we can!