More on Battery Life

After a week of use, a few statistics can be developed regarding the average use of the iPad and its battery capacity during archaeological excavation.  Table 1 below identifies my tracking of the battery life used each day for the ten iPads. iPads 5, 9 and 10 were only used for the cemetery survey work which only occurred on Thursday and Friday last week.  In addition, Friday afternoon (7/12) was truncated by a lecture and the water screening demonstration so only represent about a 5-hour day.  Due to a glitch, iPads 1 and 2 were not charged the night of 7/9/2013 and the students started 50x50-cm shovel tests (with traditional paper forms) the morning of 7/10/2013 while the units were charging.  iPad 4 was at 8% at 1 pm on 7/10/2013 when it was recharged, therefore only representing about a 4.5 hour work day.

TABLE 1. iPad BATTERY LIFE USED OVER A FIVE-DAY FIELD TEST IN JULY

	7/9/2013			7/10/2013
iPad#	Start	End	Battery Life Used	Start	End	Battery Life Used
1	78	42	36	100	45	55
2	68	3	65	100	84	16
3	100	86	14	86	75	11
4	100	61	39	61	8	53
5	100	100	0	100	100	0
6	81	56	25	100	55	45
7	76	55	21	100	100	0
8	100	59	41	100	67	33
9	100	100	0	100	100	0
10	100	100	0	100	100	0
	7/11/2013			7/12/2013
iPad#	Start	End	Battery Life Used	Start	End	Battery Life Used
1	100	73	27	100	97	3
2	100	50	50	100	79	21
3	100	93	7	100	100	0
4	100	42	58	100	82	18
5	99	24	75	100	37	63
6	100	60	40	100	88	12
7	100	37	63	100	50	50
8	100	68	32	100	48	52
9	100	14	86	100	41	59
10	99	22	77	100	38	62
	7/13/2013
iPad#	Start	End	Battery Life Used
1	100	60	40
2	100	79	21
3	100	99	1
4	100	98	2
5	100	100	0
6	100	40	60
7	100	2	98
8	100	19	81
9	100	100	0
10	100	100	0

As shown in the Table, the cemetery monument recording work, which generates many more forms and digital images, uses up a lot more battery life.  For the two days in which they recorded cemetery headstones, the student's iPads used between 59% and 86% of battery life.  Because Friday was only a five-hour day, and Thursday was a training day when the new crews were getting oriented to the recording strategy, the average battery use might be a bit more for a fully trained crew over an 8 hour workday.  The average for Thursday of 79.3% is probably conservative.  

Ignoring the partial days and charging glitches, the other seven iPads measurements over the five days is 35 observations of battery use.  The average use was 34.0% of the battery with a standard deviation of 24.26.  There was a significant range between no use (the iPad was not used) and 98% of battery use. As iPads are tied to particular excavation units, no use indicates that those units were not excavated that day.  Excavation tasks included filling out the four-page level form, taking images, and some intensive use of iDraw to map the World War I railroad grade. I think a fully trained professional field crew (excavating at a rate of 2 10-cm levels per person per day) will likely generate more forms and perhaps use more battery life depending on the complexity of the site.   Even so, there appears to be plenty of capacity for excavation forms and digital images. This is consistent with the results from other projects, such as the Pyla-Koutsopetria Archaeological Project on Cyprus and the E'se'get Archaeology Project in Nova Scotia.

House Floors, the Spruce Mill, and Other Excavation Notes

Concentration of beads being discovered at the Little Prouxl House Site.

Hearth exposed below house floor
(about 70 cm top to bottom -- west is up)

Over the past two weeks we have been exploring the house floor of the Little Proulx House Site and clearing more units to expand on these excavations.  There have been a number of notable finds, including a cluster of about 70 white beads (what appear to be small, hot-tumbled tube beads) in the southwest corner of one of the excavation units.  The location of this cluster is mapped using the annotation tool on the PDF Expert program. Just to the west of this, a concentration of baked clay (or "bisque" as it is used in the Pacific Northwest, probably from the house fire when it burned), a charred beam, and concentrations of  bisque and charcoal likely associated with the destruction of the house.  In one area nearby, a nicely-defined hearth with a charcoal-black rim and reddish-brown interior was discovered below the clay floor.  This may be a hearth that preceded the construction of the house or an earlier iteration of the structure before the clay floor was
laid down.

We are also shovel probing the Spruce Mill Area, exploring some of the magnetic anomalies identified by Kendal McDonald a few weeks ago.  The probes are about 40 cm in diameter and are dug to at least 50 cm in depth.  The first week of probing we found many interesting strata tied to fill associated with the World War I mill site and later uses of the property for aviation and other U.S. Army and City of Vancouver uses. We found surprisingly few metal objects or other sources that could be tied to the anomalies.  This past week we used a metal detector to really home in on the magnetic sources and were rewarded with many metal objects, including cast spikes, a likely aviation fuel line, and other objects.

Excavation of a shovel probe at the Spruce Mill cut-up mill site.
Pearson Air Museum, including the repurposed World War I hanger  in the background.

Back at the dig site, we used iDraw to map the top of one of the World War I Spruce Mill spur lines that rest above the Little Prouxl House Site.  Besides being an excellent training excercise, we are troubleshooting the use of iDraw for illustration of plan and profile maps.

Battery Life in the Field

One of the concerns raised by some with the use of tablets in the field was battery life and if the tablets would last through an entire day of field recording. I am happy to report that battery usage during excavation is about 20-40% during the day depending on the number of forms worked on. While the school is digging more slowly than a professional crew in the field, it appears that there is plenty of juice to record excavation data without having a supplemental source or having to swap out units.

In contrast, the cemetery recording project uses up an entire battery each day. One tablet ran out of juice before the final photos of monuments were recorded. This is undoubtedly due to the much larger number of forms created each day during cemetery recording.

By recording battery life each day, we should be able to get some metrics on the number of forms generated contrasted with battery expenditure. This week I will collect some data.

Survey Crew Starts Work at Spruce Mill

As part of the Field school, the students learn skills in field surveying to discover and record archaeological sites, including basic orienteering and gps, pedestrian and subsurface shovel probing, and mapping and site recording.  This week, a quarter of the field school started this portion of the course under the direction of Tony Hofkamp.  The site of this course is the field east of the reconstructed fur-trade fort and west of Pearson Air Museum.  This was the location of the World War I Spruce cut-up mill.

Last week Kendal McDonald (Z-Too Archaeogeophysical Prospection and Applied Archaeological Research) collected remote sensing data from the Spruce Mill area using her gradiometer (see Remote Sensing post from last week).  She was able to get us some preliminary results from the 160 m long north-south by 20 m wide transect we set up across the Cut-up mill. There are some dramatic patterns in magnetic anomalies that the survey crew will explore over the next four weeks.

While we excavated over a dozen probes this week, we have not had good fortune hitting the source of some of the anomalies. Next week I plan to use a metal detector to refine the locations for probes

Kendal McDonald shows Field School the results of the
Gradiometer Survey in the Field Laboratory

Magnetometer Results laid out on the Laboratory Floor.  Some of the strong positive-negative
linear anomalies may be buried cables for aircraft ties from the later airport.

Bag Catalogs and the Field Laboratory

Yesterday we started our field laboratory portion of the course.  Students will cycle through the field lab to gain basic skills in organizing, cleaning, and error-checking the collections and archival materials. When we were designing the digital forms we made the conscious decision to only maintain a bag catalog tied to the level and feature forms and to not have a separate bag catalog for artifact bags collected from each unit.  While this removes an aspect of redundancy which is designed to avoid errors, it was thought that the digital forms would facilitate the creation of a bag catalog in the field laboratory to assist in error checking, and building a site-wide artifact catalog.  On Monday, while the Field School rested, I explored how to go from the adobe forms to excel to create a usable bag catalog. The pdf forms can be extracted to an excel spreadsheet with ease and it is simple to extract the data from each level form as a row (single line on a relational database) tied to individual units.  To then use these data to create an inventory of bags collected, I wrote a short macro using Visual Basic which primarily uses a For Next routine to collect the six variables collected for each bag, including its bag number, type of artifact (e.g., beads, transferprint ceramic, etc.), the field count of artifacts in the bag, and if it was point-provenienced, the northing, easting, and elevation of that object.  The routine simply copies these data for each level form listed on the excel worksheet as a line to a new bag catalog worksheet.  At this point there is still a bit of cleanup necessary to sort the bags to remove blank spaces between levels and I had to add a "level" field that we are adding by hand in the lab during error checking.  When I get a free moment I will work on the macro to attempt to further streamline these processes.  We are starting to use these "bag catalogs" in the field lab to create lot and specimen numbers to track the collections through the cleaning, analysis, and cataloging process.  Stay tuned for how it will work out!

Remote Sensing

Today Kendal McDonald will finish a magnetometer survey of the World War I Spruce Mill site east of the reconstructed fort. On Wednesday, Kendal conducted a workshop with the students on the main parade ground and then collected data from a 20 X 20 m square on the suspected site of the original US Army flag pole. Kendal's magnetometer is a Geometrics G-858 dual sensor cesium magnetometer configured as a gradiometer. She records the magnetic signature of the sediments she walks over and contrasts it with the magnetic "noise" of overhead power lines, solar radiation, and other intrusive magnetic disturbance. The resulting magnetic gradient between the two is used to look for changes in the sediment magnetic signature tied to metal objects, old pits, hearths, and foundations. 

Besides the flag pole location, we hope to find foundations, rail lines and other remains of the spruce mill. The mill cut spruce logged from the coast range into pieces suitable for making aircraft during the Great War.

Upon us all a little rain must fall

Today we started our second week in the field at the Fort Vancouver Village. It rained quite a bit over our Sunday-Monday "weekend" and continued off and on with showers today. While there was never a steady rain, there were lots of drips off the shelters and students got to try out their rain gear.

The iPads held up nicely in moist conditions and we verified that it is possible to use them inside a clear sealable plastic bag. On Monday I updated the form templates to correct a glitch in the other materials observed but not collected category. I also developed a simple photo log form to collect the information we need for each iPads photo images.

The crew on Block L (Little Prouxl's House) started removing 5 cm of the house floor. They are finding some Hudson's Bay Company artifacts and some larger animal bones tied to the house. Some remnants of the gray clay floor remain from last year and the students are removing these patches. 

In the morning we had a visit from some Oregon Museum of Science and Industry (OMSI) campers who are learning about the science of archaeology for 1/2 a week and then heading out to John Day fossil beds for 1/2 a week.

The campers helped screen and the students helped to explain some of the common field tasks like excavation and plan mapping. The students also showed the use of the iPads in field recording.