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Planetary News: Mars (2005)The Planetary Society's Mars Analog Blog:
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Credit: Troy Hudson |
Starry, Starry Night.
Eastern side of Frank Hill 2:30am
Oddly enough, this may well be the most comfortable night I’ve yet spent out in the field…and I’m sleeping in the back seat of a small truck.
I left the station at around 11:00pm tonight and drove out to the far side of Frank Hill. My hope was to be able to set up all my instruments and look at the soil throughout a sunrise event on a slope that faces East. I admit that I might have done better to locate a field site before the sun went down, but I think I’ve found one that’ll prove useful enough.
It took me about half an hour to unload and set up all my equipment once I found a suitable spot. I’m on a shallow slope (about 15 degrees, possibly 20) on the eastern side of a low lobe of Frank Hill. According to my compass and my Equinox celestial navigation program, the sun should rise at an azimuth of ESE at 7:30am. The trick is to make sure that none of the equipment or the truck blocks the rising sun…I don’t want any artificial shadows.
It’s a positively balmy night. I think it was at least 10°C until midnight when the wind finally picked up. I was out there fiddling with the TECP for about forty-five minutes after everything else was set up and running. It’s being most aggravating. It didn’t work in the field yesterday, but did when I took it back to the station. And now that I’m back in the field again, it’s behaving strangely. Through various experimentation, I was able to whittle down the possibilities of what’s going wrong. Originally, I thought it was the order in which components were connected. Then I thought it might have been a grounding issue. But it turns out that there’s some sort of interference going on in the wires leading to the TECP. When they’re all bundled up in a particular way, it works fine. But when you stretch out the line to put the device into your soil of interest, the loops of cable disappear and it flakes out. There’s also a correlation with whether or not I’m holding the bundle of cables in my hand or not. Definitely some sort of capacitance/inductance issue with the cables. I’ll have to take this up with the Phoenix team when I get back to JPL. They’ll want to know about this so we can avoid any similar issues throughout the rest of testing and integration, and when the thing finally gets to the surface of Mars.
Work setup on frank hill
Credit: Troy Hudson |
I packed the TECP back up and put it away. I have a mind to think it’ll stay that way until I leave here. One less thing to worry about and I don’t think I have enough knowledge about how it’s put together to develop a workable, robust solution. Besides, it’s late, I’m tired, and I’m only getting sleep in fifty-minute intervals as I take my readings.
The KD2 is working perfectly. It would be great for future excursions if the guys at Decagon could produce a one-off instrument which can log data at regular intervals so I don’t have to keep getting up. I’ll take that up with them when I get back also.
I’ve got a HOBO datalogger from OnSet corporation deployed to monitor air temperature and humidity. This saves me from having to get the Kestrel out and take readings every hour, which means more sleep for me!
HOBO datalogger
Credit: Troy Hudson |
Although I must say, being away from the lights of the station, alone out here in this most desolate of deserts, with naught but the innumerable stars for company, I hardly want to sleep. I’d be happy just gazing at the stars all night were it a bit warmer. Still, the view from within the truck is quite nice.
Current Mood: mellow
Current Music: absolute silence.
Yungay Station 10:00 am
I’ve heard tell that some people can train themselves to sleep for a few hours at a time through the course of a day, wake up on demand, and get things done without an eight hour hiatus for sleep. I’m inclined to believe that since last night’s hourly awakenings to take readings haven’t seemed to adversely affect my morning at all. Quite the contrary, I’m wide awake and feeling incredibly productive. I’ve been able to reduce all of my data from last night already, I’ve reformatted my pictures, and even put a lot of them into a quick power-point presentation to show Chris et al.
The sunrise was quite beautiful. Moonrise just before it was better. I saw a beautiful silver crescent creep above the mountains just as astronomical twilight was ending. The sun was still about 12° below the horizon and the sky was just coming light, which should make for an awesome picture. It’s moments like that when I wish I had a much better digital camera…but such events are rare enough to make such a purchase somewhat extravagant.
Frank Hill Sunrise
Credit: Troy Hudson |
The data I got were about what I expected. Temperature of the air and soil shot up as soon as the sun hit them, while the relative humidity plummeted. There’s an old phrase that says things are always darkest just before the sunrise. Well, that’s hardly true. But things are certainly coldest just before sunrise. Although last night was warmer than the previous few we’ve had here, it still got below freezing. But this was only in the last hour to hour and a half before sunrise. It’s during this time that the air loses the greatest amount of its moisture carrying capacity, relative to the amount of absolute moisture it contains. The relative humidity shoots up and you get condensation if it reaches 100%. Well, last night’s pre-dawn RH values were only in the range of about 35% +/- 5%. According to Chris, this is less moisture than one occasionally sees during the winter here, especially when you do get the fog we’re eventually hoping to experience. Even after last night’s air temperature dropped below 0°C though, the relative humidity stayed roughly constant at 35% until the sun rose, at which time it dropped to less than 10% in two hours.
Chris says that it’s very difficult to predict when you’re going to get a fog event out here. We don’t have that extensive of a meteorological baseline to be able to extract any predictive power. It would be nice if you could say, “If the relative humidity is at least 80% by 2 hours before sunrise, you’ll get a fog event.” And even better if we could predict what nights are likely to get that 80% relative humidity. As it is, I’ll just have to get up before dawn every day and see if it’s foggy. Or perhaps I’ll just set up my equipment like I did tonight for the remainder of my time here.
I’m already getting some great ideas for how I could improve these measurements were I to come back to this field site. For one, I really don’t think this infrared camera is working that well for water detection. Through the camera, I’m essentially seeing a grayscale, low-resolution, pixelated version of what I can see with my eye. Granted, this is a near infrared camera, which looks in the 900 to 1700 nanometer region, while my eye is in the 450 to 770 range. But still, wet soil looks dark. And if it looks like it’s dried up to my eye, that’s how it looks to the camera, too.
We’d hoped that the strong water absorption feature at 1450 nm would stand out in these images and make the camera see black spots wherever there was water. But the band we’re looking in is too broad, and the filter we were able to obtain prior to leaving is centered at 1480 nm. It’s a moderately wide-band filter, so it still sees some of the effect of the water line, but a narrow filter exactly centered on 1450 would be much better.
Better still might be a camera that sees in the thermal infrared. Experiments from a few days ago showed me that the soil surface was sensibly colder than the surrounding, unwetted soil far after and visible trace of the water disappeared. It took 40 minutes to come to equilibrium when the soil was in full sun.
Chris is interested if rock-free soil retains more moisture than nearby soil with a pavement cover of small stones. If I had more than one KD2 needle probe, I’d attempt to sense the properties of both during a wetting event both in the middle of the day and through a sunrise event (this latter case most accurately duplicating the conditions of an early morning fog.) Temperature seems to vary much more than thermal properties during a wetting event, so if I just want to sense the surface I could get a nice spatial resolution over a large area if I had a long-wavelength thermal infrared camera. These are quite common, so maybe next year.
I think I’ll stay up for a while until the afternoon winds pick up, when the temperature drops a bit and it’s nice and breezy, and then take a nap. In all, a very good night’s worth of field observing.
Current Mood: Accomplished
Current Music: Forbidden Broadway: They Shouldn’t Be in Pictures
Yungay Station 3:30pm
A bit of excitement...
Just a quick update. The Mars Organic Detection team seems to have nearly completed setup of their rather impressive lab. They’re still working on getting the vortex cooler to work at full efficiency, there seems to be a problem with the air compressor.
There has been a film crew from Discovery Canada here around the station for a few days. They’re most interested in the life detection experiments, so haven’t been that interested in me. Which is fine from my perspective -- I get to focus on my work rather than reiterating interviews and pretending to do science while they do take after take. Not that they’re a bad bunch…but you just can’t capture the excitement of real scientific research on film…just doesn’t work. Ever seen anything by Hollywood where you get to see a research lab with its clean desks, state of the art equipment, and no wires anywhere? Well, it just ain’t like that, Lucy.
The film crew brought a helicopter to the station today. They’re going to be viewing some of the field sites from the air. I imagine they look quite good from up there and I wish we all had the chance to go for a ride. Allison will be getting to go, as well as Chris. They’re the stars of this particular production.
It would be really cool if the IR camera or some other method allowed us to remotely characterize or at least discriminate between various sites from the air. Then perhaps we could get a helicopter next year and get some real science out of it. Then again, even if we don’t, it’s a great way to get around and go to the various sites without having to worry about the flaky 4-wheel drive on some of these trucks.
It’s pretty interesting – the helicopter kicks up almost no dust when flying over the undisturbed desert, but kicks up a hell of a lot when passing over a road or a patch of well-trodden ground at the station. Just goes to show you how well indurated and encrusted the desert soil is around here.
Current Mood: thoughtful
Current Music: thup thup thup thup thup thup thup thup thup
Yungay Station 8:00pm
I’ve got my work cut out for me. I’ve begun doing analysis on the water potential of my soil samples using the WP4 instrument from Decagon devices. You know, it’s really easy in some cases to collect huge numbers of samples that rapidly forms a pile of work waiting to be analyzed. I started working with the WP4 this afternoon around noon and have only made it through about one third of my samples so far. (WP4, WP4 and hotplate).
It takes about 12 minutes for the samples to equilibrate in temperature, and then about another 10 minutes do complete the water potential analysis. My part in the procedure is very simple: I insert the sample and close the tray, the equilibration begins. Once it’s equilibrated, I turn a knob and the measurement begins. The machine beeps when it’s done. Simple, right? Well, yes…but it means I can’t go anywhere or do anything else if I want to be efficient with my time. I have to be here to flip those switches and change the samples.
I have about 20 samples to go through today and I’ll be collecting another 10 or so tomorrow morning on Rock Garden Hill in the shade. Which in turn means that depending on how much I get analyzed tonight after dinner, I’ll be spending most of tomorrow in front of this machine. I hope the numbers I get are useful.
Fortunately, or not, depending on how you look at it, I can’t do gravimetric analyses here at the station. Earlier today I set up a hot plate to heat my samples to over 100°C to drive off whatever water they contained. I measured the sample’s mass before and after the heating and had hoped to determine the total amount of water present in the unheated sample. But we don’t have a balance precise enough to see the incredibly small variations we’re talking about here. At best, I can say that the water content of these soils is less than 0.67% by weight. For a terrestrial soil, that is incredibly dry, even in a desert. You’d probably get the same amount if you tested the water content of the sand in a dune. Most of it’s adsorbed surface films.
So, I can’t do gravimetric analyses here. Pity, because now those samples that I heated are useless. But fortunately I discovered this using samples from just here around the station and so they aren’t that scientifically valuable anyhow. I’ll just try to seal up and preserve the rest of them for a trip back to JPL where I have a balance with much higher precision.
The WP4 is a pretty neat instrument, though. It’s expensive, so I don’t think we could justify purchasing one. But once all the data’s been collected we’ll see if the water potential data is useful. Water potential is made up of 4 components: gravimetric, osmotic, matric, and pressure. These four contribute to the potential energy of water in a system. Gravimetric potential is just what you’d expect – the potential of a mass of water to want to move to lower energy by coming closer to the center of the earth. Pressure potential is related to gravimetric and can be caused by gravity, but it can also be entirely lateral in direction. Think of it as hydraulic head, usually only significant over long distances.
Osmotic potential is caused by the tendency of water to move so as to equalize solute concentration (salts, organics, anything that dissolves in water). Water will move from an area of low solute concentration to an area of high concentration so the dilutions of the two areas become equal. Matric potential can be thought of as the surface tension energy of the system. The water wets the surfaces of the soil grains and allows the soil to retain water. Matric potential is measured in units of pressure (as are the other potentials) and is always negative. Pressure potential, on the other hand, is always positive, so the two cannot coexist in the same soil at the same time.
The WP4 measures the combined effects of matric and osmotic potentials and reports the values as a negative pressure in megapascals. The way it does this is kind of clever. First, it seals the sample in a small chamber and allows the whole system to come to equilibrium. While this is going in, whatever water is in the sample equilibrates with the head space above the sample. A small fan helps this process complete more quickly. Then, to take a reading, the WP4 has a chilled mirror hygrometer that determines the relative humidity of the vapor in the head space. A chilled-mirror hygrometer works by using an electric cooling unit to reduce the temperature of a mirror until dew or frost forms on its surface. The frost/dew point temperature bears a well-known relation to the relative moisture content of the air. The drier the air, the cooler the mirror has to be before condensation takes place. To monitor whether or not condensation has happened, a small laser bounces of the mirror into a photodetector. As frost or dew forms, the intensity of the reflected light is reduced, and the transition is quite sharp. The relationship between water potential and vapor pressure is well defined also, being proportional to the logarithm of the ratio of actual vapor pressure to the saturation vapor pressure. All the math is internalized on chips within the WP4, so the measurement process is simple. But it’s necessary to understand the theory behind it all in order to make any scientific sense of the numbers the machine returns.
It’s time to have dinner, but I’ll be constantly swapping samples until I hit the sack tonight. In the intervals, I’ll either be eating dinner, reading David Sedaris, or fiddling with the data from last night’s IR camera observations.
Current Mood: mellowly overwhelmed
Current Music: Paul Oakenfold, Composure
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