Identifying Wind Streaks

In my last post I described a student project to figure if there are global wind patterns on Mars. Now, I have a few things to say about searching for wind streaks.

When searching for wind streaks it is important to correctly identify what you see. There are some features that might confuse you. For example, here is an impact crater


On the west side of the crater is something that looks like a bright, mostly vertical feature. Most wind streaks are bright, so is this a wind streak? No. This is bright feature is the result of strong sunlight reflecting off the crater rim. The shape of this bright feature doesn't match the teardrop shape we saw on authentic wind streaks. From the shape of the above bright feature you can't make sense of what way the wind is blowing. The wind streak should trail off on the downwind (leeward) side of the feature, not go along the side of the feature. Another clue that is a bright feature is a function of the sun is that there is a shadow on the other side of the crater.

Not everything that has a teardrop shape is a wind streak.


The behavior (and the physics) of wind blown dust is very similar to silt and dirt traveling downstream with a river. In both cases you have material in suspension being carried along. Depending on turbulence material can be carried away or deposited. So, features formed by wind can look like features formed by rivers. When making an identification like this pay attention to the surrounding area and use it to help determine if you're in, for example, a riverbed.

Wind streaks tend to be pretty thing thin. So, they have don't really stick up above the surrounding terrain. However, many teardrop shaped features formed by flowing water have a significant elevation profile.


The dust and sand that forms a wind streak tends to have a very small thermal inertia value. However, there are two problems with using thermal inertial to identify wind streaks. First, the thermal inertial detector has, compared the the Viking camera, fairly poor resolution. Most wind streaks are smaller then a single thermal inertia pixel. So, the thermal inertia value combines all the wind streak and a bunch of surrounding terrain instead of having several values inside the wind streak like you'd need. Second, if a wind streak is thin enough the thermal inertia value of the underlying surface is also detected. While a very thin layer of surface dust might cool quickly, perhaps the rock underneath received enough sunlight to heat up and will take a long time to cool down. So, the received thermal inertia value is a combination of both the dust and the rock.

The dust and sand that forms a wind streak tends to have a very small thermal inertia value. However, there are two problems with using thermal inertial to identify wind streaks. First, the thermal inertial detector has, compared the the Viking camera, fairly poor resolution. Most wind streaks are smaller then a single thermal inertia pixel. So, the thermal inertia value combines all the wind streak and a bunch of surrounding terrain instead of having several values inside the wind streak like you'd need. Second, if a wind streak is thin enough the thermal inertia value of the underlying surface is also detected. While a very thin layer of surface dust might cool quickly, perhaps the rock underneath received enough sunlight to heat up and will take a long time to cool down. So, the received thermal inertia value is a combination of both the dust and the rock.

Even though wind streaks are a relatively easy feature to identify, it is possible to get it wrong. When you study a region always think about how the sun is illuminating the scene. When you're trying to identify a small feature, keep the surrounding context in mind. Your scientific reputation depends in part on how correctly you identify features.

Project: Global Martian Wind Patterns

Students will have to complete specific planetary exploration projects. This is a description of one such project. Note that I'm in the process of changing the name of the software from GeoVirgil to Planetary Exploration Program (PEP). They are the very same program. I hope the two names don't cause too much confustion.
If you know something about analyzing Martian winds streaks, your comments and suggestions on this project idea are most welcome!!!

The goal of this project is to map Martian global wind patterns by mapping Martian wind streaks. On Mars are there large regional wind patterns or is it all driven by local events?
In my small backyard, it seems like the wind direction is pretty random. Sometimes it is from one direction, sometimes another. However, there are place on Earth where I know the winds are more regular. A good example is the Atlantic Trade Winds. Just north of the equator the wind generally blows east to west from the "old world" to the new. By the mid-atlantic states the winds blow west to east all the way to Europe. When ships where powered by sail the Trade Winds where the key to travel. Does Mars have Trade Winds?

If you look hard, you can find wind streaks on Mars.


This image has a number of wind streaks. They are all bright tear-drop shaped features to the southwest of the circular impact craters. Wind streaks tell us several important things. First, if there is wind then there must be an atmosphere. You won't find wind streaks on the Moon. Second, there must be some material to streak. Something small and light like dust or sand must exist. This further assumes there must be a source of such material, such as extensive volcanic emissions or some way to break rock down into dust. Finally, there must be enough temperature variation in the atmosphere to cause wind.

In the above image crater rims are disturbing the wind causing bright streaks to form on the leeward (downwind) side. There are two ways to form streaks. Either the disturbed wind can deposit material or it can scour away material. On Mars both happen. On Mars some streaks are bright and some are dark.

Here's a close up image of a wind streak:


In this image I greatly increased contrast by creating a second Brightness And Contrast Filter for the Global Imagery layer.

PEP has a tool to help map directional fields like wind streaks or water flow. Click on the Tools menu option and select "Draw Arrows Panel". Use this panel to create an arrow showing the direction of the wind streaks.


Now, zoom out to see a large region of the planet. Naturally you won't be able to see the wind streaks any more because they'll be must to small. However, the arrow remains showing the wind direction.


If you search the Martian globe for wind streaks and mark each field you'll end up with record of the global winds. Do you see the equivalence of Trade Winds. Are the streaks formed by local events that don't suggest any global patterns?

Email To Students

Here's the email I sent to the students after our first meeting:

Thanks for taking the time after school today to learn more about the project. If you have any questions or concerns feel free to send me at email.

My blog on the project can be found at http://planetarydata.blogspot.com/. I hope you'll take the time to occasionally read it and post comments. I hope as we get into the project you'll take a few minutes and write posts and email them to me. To provide some annonimity, the blog won't have either the school's name or your name. However, I may use your initials.

There is an effort at NASA to figure out if it is possible to get planetary data into the classroom, engage students and provide "powerful learning experiences". There are lots of pieces to this very hard problem. NASA has tons of data with more always coming in. Planetary scientist have ideas regarding projects that might be suitable for high school students. Teacher have lots of classroom exercises. I can pound out software to do most anything. But until actual students like yourselves are involved, we don't know if we have anything really valuable.
From most people's perspective (including mine!), the most important things to come out of this project will be your impressions, comments and suggestions. To make sure I get some feedback from each of you, I'll eventually be emailing some surveys to gauge your backgrounds and get comments. Don't worry about being overly critical. It is from your brutal honesty that we can make improvements and reach our goal of having something that can make a difference.

First Contact

My Planetary Exploration Program (PEP) installed and runs fine on the high school's computer. The biggest problem is the computers don't have a DVD drive, only CD. On my install DVD I include about 3GB of NASA data. I couldn't use that disc and only had time to install 1 CD of data. Are there lots of people or schools that might want to run PEP but only have a CD drive? I have no idea, but next time I visit the school I'll bring my portable DVD drive.
The machines in the Science Department's Computer Lab are Dell Optiplex GX280 with a 2.79 GHz processor and 504MB of memory. More memory would definately help, but these machines should be sufficient. I tested the joystick by flying around Mars and that worked well.

I briefly met with four students who will be working on planetary exploration projects. I have them a pretty quick demo of both the 2D map and the 3D fly-over. It was clearly well received! I also described the possible projects briefly and the students were interested. I'll blog about the possible projects soon.
The students must complete their Science Fair projects by the end of Feb. So, I'd like to have working on the projects at the beginning of Jan. So I'll have to meet with the students a few times starting right after Thanksgiving. Over about 4 sessions I'll give a really brief overview of how planets work, review how to use PEP and, by the end, hand out details on each project.
All four students have email addresses. That wouldn't have been the case a few years ago. It will make communication so much easier! They also mostly have pretty good home computers (512MB ram, DVD drives) and should be able to run PEP at home.

My Project In An Urban High School

Many of the early posts in this blog will discuss a volunteer project I'm running in a nearby high school. Since the school, teachers and students haven't asked to be put in a blog, I won't be using anyone's actual name. For background, the high school is in the Boston, Massachusetts area in a town or city that is on the subway. Its a big urban school with a pretty diverse population. Every year they send students to some students to top schools and have lots of kids who can't pass the standardized tests.

At the high school all students that take a "real" science must complete in the school's annual Science Fair. This is important because it makes getting students to participate in my project very easy. Rather than the student having to think up some project on their own, I show up with a bunch of pre-packaged Science Fair projects. They pick one and I provide the software, data and mentoring. They put in their own hard work and have a cool project to show for it.
Without the Science Fair requirement, I'm not sure how I'd get the kids to sign up for an after school program that requires a bunch of work. Kids in this school are pretty busy. Most of them have part-time jobs. Since they are taking a "real" science course, they are also on the college track. As you might expect, they are also involved in a bunch of school activites in part to improve the college applications.

I've done several projects similar to this. In the past, students worked in pairs. It is easy to get students to sign up for something new if they aren't going to be working alone. Typically, we've had a total of 8 to 10 students have been allowed to participate.

Today, we've got the remnants of huricane Wilma giving us lots of wind and rain. But, the schools are open. This afternoon I'll try to install my Plantery Exploration Program (PEP) on their computers. At the school, the Science Department has their own computer lab. This summer, they got new machines. In my next blog post I'll let you know how it went.