Tag Archives: Aerial photography

Traditional Strategy and New Techniques

by Frands Herschend

Strip (off the plough soil), map (the patterns you see) and sample (material from mapped structures) – is an archaeological field strategy applied to settlement remains in agricultural land, where crops have been growing for centuries. Ultimately, the method has become prolific, because of the gradual shift in the use of the cultural landscape. This shift made arable land more important and organized not least by means of roads. Consequently, farms were moved out of the farmland when possible. In Iron Age, on the other hand, arable land was less important, while grassland and meadows contributed substantially to subsistence. Not surprisingly, a rational Iron Age farm situation was in the centre of the farm’s agricultural area. Few roads were needed.

In Kvarnbo, change has been model, and today, the farms at Johannisberg are situated next to and above the arable land in which the Iron Age Kvarnbo hall stood on its small drained hillock.

When the excavations were planned, the strip, map and sample method was the obvious choice. But there are different way of stripping, mapping and sampling, and at Kvarnbo we have introduced a new mapping method in order to develop the general method. The testbed was successful during the test excavations in 2014, and in 2016, this mapping method was developed to become a routine.

Except for a handful of GPS reference points defining some of the test pits before the excavations started (see here), nine main reference points were defined after the top soil was stripped off in the area of over 1000 m2, and complemented with 183 reference points inside of that area. Supported by these, all (georeferenced) exact measurements, plans and sections are based on photographic 3D models. Also, a large scale plan was made with a drone during a 10 minute photo session and its orthographic projection, printed as an overview, has enabled the team to orientate itself on the site.

New techniques

Archaeological documentation goes hand in hand with interpretation. Description dominate fieldwork without excluding interpretation, and in the field, ocular observation is the general mode of perception: either you see something of you don’t. Later on, during the report writing process, interpretation and lab results dominate in order to answer the question: what cultural phenomena have we excavated? The problem in field archaeology is not what one observes, the problem is that which cannot be seen.

Overlapping features in the trench of 2014

In this section from the trial excavations of 2014, one can see archaeological features from Late Iron Age (A12 and A13) been transected by more modern plough furrow (A18).

For instance, looking at plough layer and plough furrows or any other depression, the point is to describe some sort of “ploughing biography” of the field as a part of the its involvement in history. It is easy to see the dark furrows when they cut into the yellow underground, but difficult to detect them at the bottom of the plough layer, and impossible higher up, although they may well exist in soil 20 centimeters or more below the surface. In fact, only by means of close observation of soil sections can one distinguish between ploughed and not ploughed soil.

Since we want to sample the contents of the different fills in postholes, we make a preliminary section of the first centimeters of the soil until, based on this section, we can dig away the plough soil, that is, the contamination of the prehistoric fill. As a result, we can, for example, conclude that the burnt clay, which represents burnt walls and was abound in the test pits, doesn’t exist in the postholes of the hall (because it was never burnt down).

So far, we have sectioned, described and interpreted c. 230 features of 273 on the c. 1000 m2 of our site. This is time consuming, but the ensuing 3D documentation is fast. On average, therefore, a team of four professional archaeologists and 2-3 amateurs can section, describe, interpret, sift and model 20-25 features per day, and sample soil for chemical and macrofossil analyses. 3D-modelling brings a new better and cheaper standard to strip, map and sample methods.


Week 5 – brief summary

Anläggningar undersöksThis week we had Daniel flying the drone over the cleaned surface, barely beating the rain, and giving us the much needed overview picture of the site. The overview picture confirms what we suspected – features are scattered over a large part of the trench and beyond the boundaries of our investigation. The majority seems to be circular post-hole like features very varying in size. A couple of centrally located features excite us with both their size, placement and relation to each other 😉 Some features can already at this stage be viewed as hearths and are mostly situated in the southernmost part of the trench. Otherwise, the surface is quite obviously dominated by plough furrows, hundreds of them, as well as a couple of long ditches transecting the entire site. We have numbered and individually photographed 246 archaeological features defined so far and have also started to make cross-sections through some of them. Investigating the features will dominate the rest of the excavation. Sadly, that will be done without help from Anton and Peter, both of whom have been with us 4 weeks and have proven themselves to be true troopers of archaeology – their effort was highly appreciated and will be missed. They left together with Jonathan and the remaining, diminished team thus has the fortune to investigate all the features no matter the weather 😀


The Mighty Hole

Soil stripping is finished! We have a trench of about 1000 square meters, of which roughly half is already manually cleaned and hidden under the tarp. There are three large mounds of soil surrounding the (mighty) trench (which are pretty good for taking overview shots 😉 ). The subsoil in the trench is quite varied; from a smooth yellow and clayish silt in the south to a  difficult and stony moraine in the middle and diabolically hard clay in the north. But archaeological features are everywhere! These are especially visible against the yellow silt in the southern side of the trench, while revealing them in the other areas requires extensive manual cleaning. Furthermore, traces of plowing are constantly present, easy to follow and generally oriented to the north-south… We have hundreds of features marked out using yellow wooden pegs. Of these a good amount will probably turn out to be just natural depressions, but many are clearly related to prehistoric use of the area. Joining these together to an understandable pattern is a challenge in which a bird-eye-view is crucial. This will be obtained through photographic 3D modelling and is the reason why we are eagerly awaiting the clouds to hide the ever-shining shine above our site 😀  schaktning

Day six (part 2)

Today was all about aerial photography which is constituting a part of the documentation at our site using 3D modelling and photogrammetry. Photogrammetry is a process that produces spatially accurate images from ordinary photographs – with these images being georectified we can produce photographic plans of our site and its stratigraphy and take accurate measurements directly from the photo (!). This method is substantially improving the archaeological documentation during excavations and seems by far the best choice for recording topographical data at an archaeological excavation 😉 I am fortunate that archaeologists at the Uppsala University in Sweden are currently developing the method for practical uses in the field and both professor Frands Herschend and dr. Daniel Löwenborg from Uppsala are on a voluntary basis involved in my project. Today’s photo-shoot using a drone was aimed at creating so-called background to all the other data we are collecting at the site.

Day 6_1As expected, we also established that the part of the trench 1 that was soaked yesterday meant archaeological features in that part being much better perceived today than the features in the dry part of the trench. Not to mention how much easier it is to dig when the soil is damp. Obtaining and combining a number of hoses into one 125 meters long hose and connecting it to the tap by the churchyard we have now a method to spray the trenches whenever there is a need instead of carrying buckets with water.

Day 6_2

Bird’s-eye view

Aerial droneThere is no question that archaeology today is not only digging holes in order to discover the traces of past people and cultures, there are so many other ways to get clues about what is underground. And I am all about testing new methods, especially, non-destructive methods, while working towards appropriate methodological approaches in the archaeological field-studies. Therefore, when my dear friend and colleague Dr Daniel Löwenborg from Uppsala university suggested testing photographing the site of Sa 14.9 with the help of aerial drone, there was no hesitation to whether we should give it a try.

Drones – unmanned aerial vehicles operated with radio-controlled handsets – are becoming increasingly popular in many kinds of scientific research and the use of drones has proven to be a great tool for, among other things, identifying archaeological sites. Drones allow archaeologists to cover huge areas of investigation very quickly meaning that f.ex mapping things can become a fairly fast and much simpler process with the help of drones. Now, it is not the drone itself that is working the miracle, it is the stuff strapped onto the drone that is the most important thing; and archaeologists are attaching cameras, video cameras, infrared sensors, magnetometers, barometers and GPS devices on drones to assist in their work.

However, we just tested the potential of using a drone photographing at Kvarnbo, because vegetation at the site right now is not really suitable for the simple aerial photographing as the field is not harvested yet and the crop is too high. Thus, it was not a work but a mere pleasure taking to the skies. In any case, as a result of “playing around” with the drone-driven camera we did come to the conclusion that the device will be used at the site later on when the conditions are right for aerial photographing in order to see hidden features. F.ex stone walls that lie beneath the surface often hinder the plants that grow above them and their outlines may be seen where plants are not growing very well. Unfortunately, this is not really the case when the season is rainy and this summer on Åland so far has not been characterized by drought. Thus, the drone and its operator will be back on Åland and taking to the skies might become a habit at Kvarnbo 😉