Bank Holiday Monday

The August Bank Holiday lived up to its reputation.  It rained, pretty much all day.  According to our rain gauge we had another centimeter and the roads were all flooded once more.  So, folks, that it is for Gorhambury for the next 11 months.  Plenty to do, however, with data processing, analysis and interpretation.

Today Ellen and I went back to site to collect the last remaining pegs.  Ellen organised us into walking back and forth across the field systematically to see if we could find my missing survey book.  On our second pass…

A very damp notebook!

A very damp notebook!

It was very soggy, but thanks to being a “rite-in-the-rain” product it looks OK and is now drying in the airing cupboard.  Yay!  Inevitably, as we were walking around picking up pegs and finding the book, it started to rain and we were soaked by the time we left.

On Sunday, I had some fun making timelapse videos.  Here is a condensed version of surveying three squares.

I did a poor job of setting it up for the GPR, but here it is anyway:

I have quickly processed the GPR data from using the large 160mhz antenna. We surveyed a block 20x40m which went over the “sinuous ditch” in the hopes we might be able to see it more clearly. We have picked up the walls that we saw with the 450mhz antenna.  In the radargrams (the vertical slices which is how the data is collected) I think I can see the ditch… but I need to check with someone more experienced at reading them.  Here are the time slices.  Note that we used a 1m spacing between lines which leads to a cruder picture.

Time slices from a 20x40m block at 1m spacing using the 160mhz antenna.

Time slices from a 20x40m block at 1m spacing using the 160mhz antenna.

I thought it would be useful to show one radargram from the day 15/16 block.  This is line 1893 which was surveyed from north to south, i.e., from the top of a block (as I usually present them) to the bottom.  Here is a screen grab from “radexplorer” showing unprocessed data.

An unprocessed radargram of line 1893.

An unprocessed radargram of line 1893.

It is very difficult to see much.  This is because most of the signal is the loud “noise” near the surface.  The first thing to do is tell the software where ground level is, i.e., the start of the first ‘loud’ reflection shown as black band at the top of the radargram.  Then we need to apply ‘gain’.  This is simply amplifying the lower reflections which are much weaker than the ones near the surface.

Line 1893 after the ground level has been input and gaining (using the autogain function in radexplorer).

Line 1893 after the ground level has been input and gaining (using the autogain function in radexplorer).

We can see much more now, but there is still a great deal of banding.  The bands are, essentially, echos and can be removed with the “background removal” function.

The processed radargram of line 1893.

The processed radargram of line 1893.

There is a great deal going on in this line of data.  Note, however, how the vertical column of echos under where I have put the label “wall” starts down into the radargram where as the column of echos where I have put “ring” starts at the top.  The “ring” is a small incipient mushroom ring which I noticed as we pushed the GPR over it.

A small incipient mushroom ring.

A small incipient mushroom ring.

If we look at the upper time slices we can see the ring:

A time slice from near the surface showing line 1893. The dark blob near the centre of the line is the mushroom ring.

A time slice from near the surface showing line 1893. The dark blob near the centre of the line is the mushroom ring.

For the wall, however, we need to look at a deeper slice.

Slice 3, 14-18ns.

Slice 3, 14-18ns.

In this slice we can see a small rectangular building showing faintly in the data. This building explains some of the things we can see in the radargram.  Remember that north is to the left of this radargram.

The arc we can see at the bottom of the top slice starting at about 27m west and going to 34m west is the northern edge of a very big mushroom ring.

A large mushroom ring.

A large mushroom ring.

The interaction between the fungus and the grass is quite complex.  The rings are showing in the radargrams probably because they are retaining water.  This can make the grass grow lush, or in extreme circumstances kill the grass.

A mushroom ring killing the grass.

A mushroom ring killing the grass.

Some of the rings merge and become quite complex.

A complex mushroom ring.

A complex mushroom ring.

And some of them cause mad photographers to get to their knees.

yummy circle

Yet another mushroom ring.

Yes, I became a bit obsessed.

Although we have finished for this season, there are lots of other things on the horizon, as well as working through all this great data.

I know I have said it before, but it is worth saying again.  Many thanks to everyone who contributed.  We collected great data, and we have found some really intriguing things.

Advertisements

2 thoughts on “Bank Holiday Monday

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s