Aerial Photographs

Report on the State Library Scanning Projects: Aerial Survey Photos of Connecticut

Providing access to the aerial photographs while ensuring their preservation has been a goal at the Connecticut State Library since the first statewide aerial survey was delivered in 1934. Researchers have always used the individual aerial photographs frequently: 27% of all items retrieved from secured collections in 2001-2002 were the prints from the 1934 aerial survey.

1934 AERIAL SURVEY OF CONNECTICUT

There have been two projects at the Connecticut State Library to preserve and provide online access to the 1934 aerial photographs. The Connecticut State Library, State Archives has 8,731 black-and-white prints from the 1934 aerial photograph flight. In addition, there are 239 mosaic panels, which were created from the individual photographs in 1934-1935.

There was no back-up copy because the nitrate negatives were destroyed long ago, there was a continual risk of damage due to wear and tear, some prints had gone missing over the years and the acidic envelopes were a poor storage option.

The State Library received 10,500 envelopes in 1934 but many envelopes were empty because a large number of photographs were deemed unusable. This could be because there were clouds in the picture or due to human error (Hartford daily courant Mar. 31, 1935 p. D3). The photographs start with number 00035 and end with 10,484. In all 8,731 photographs were available for scanning. Because the flight lines overlap by 60% and because photographs were taken every 25 seconds there is sufficient coverage that every area of the state is adequately represented.

SCANNING THE 1934 MOSAIC PANELS

The first effort was a collaboration in 2003 with the Map and Geographic Information Center (MAGIC) at the Homer Babbidge Library of the University of Connecticut to have the 239 mosaic panels scanned. The mosaic panels had a tic mark in each corner that indicated the latitude and longitude of that point, which was a help in geo-referencing them. Ben Smith, a Master Degree student at the university did this work. It wasn’t as easy as we hoped. Along the shoreline and the borders, he had to look for road intersections or buildings to get the panels to line up properly.

The mosaic panels were scanned by DataVault. Scanned at 400 dots per inch (dpi), the 239 mosaic panels created files of about 100 megabytes each, and when merged, created a 27 gigabyte file. This file has been compressed using a 'wavelet' compression and now the 239 panels appear as one seamless image. Users can zoom in on a point and move around from one end of the state to the other. Tips are available on Using the Mosaics and Maps on UConn Web Sites and use Internet Explorer to view the 1934 Aerial Mosaic Online.

However, because the mosaic panels were not as sharply focused as the individual photographs, researchers continued to use the individual prints heavily. It was considered important to proceed with a project to preserve and improve access to them.

SCANNING THE 8,731 PRINTS FROM 1934 AERIAL SURVEY

A further motivation was the fact that properly made and properly stored photographic materials have a life expectancy of 500 years whereas the successful long-term storage of digital images is still the subject of much debate.

Therefore, the State Library conducted a project to create new negatives, a set of new copy prints for use, and scanned images of the 8,731 individual photographs. Funding for this project was provided by the Historic Documents Preservation Program of the Connecticut State Library, which also contributed to the scanning of the mosaic panels.

In 2005-2006, the prints were sent to the Chicago Albumen Works where the first step was to scan them at 1270 dpi. This high resolution level was chosen because aerial photographs contain many fine details and subtle tones or shades of grey. It was very important to make faithful copies of the original prints. The high-resolution scans, which have been compressed for public online access, have given us the accuracy we hoped for.

One of the great challenges in copying a photograph is accurately capturing all the tones or shades of grey. The new negatives were made from the digital images using a machine called a Light Valve Technology Film Recorder. This machine exposed the negative film based on the tone values captured by the scanner. The LVT can be calibrated to minimize the loss of the light tones without making the dark tones too dark, providing a more faithful copy than traditional photographic duplication could do. The new copy prints were made from the negatives in the traditional way.

A grey scale bar was used when scanning the photographs as a way to judge that we produced a reasonably accurate copy. With the right software, the scanned photograph with the grey scale bar can be compared with the scan of an official grey scale bar to judge how accurately the shades of grey are printed.

Researchers can use the grey scale bar, along with the National Archives and Records Administration Monitor Adjustment Target to adjust the contrast and brightness of their computer monitors so that the scans of the photographs look their best.

NORTH ORIENTATION OF THE 1934 PHOTOGRAPHS

We deliberately scanned about half the photographs with the photograph numbers upside down in the bottom left corner. In modern aerial photographs, the north portion of the image is always at the top of the photograph when the number is in the top right-hand corner. But that is not true of the 1934 aerial photographs.

In 1934, the airplanes flew first north, then south, in a grid pattern and the north/south orientation of the film changed as the plane changed directions. The numbers were printed in the same corner of the film regardless of where north was on the image. Thus for some 1934 aerial photographs, north is at the top when the photographs number is printed in the top right corner. But for other photographs north is at the top when the number is upside-down at the bottom left.

The quality control steps, performed by Steve Rice and John Lenehan, included viewing all 8,731 sets, which consisted of an original print, a negative, a copy print and a scanned image, to look for obvious errors such as scratches or blurring. Ten percent of the sets were re-examined at great length, first under magnification to check for sharpness of the details and fidelity to the original print. Then, the negative was measured with a densitometer and the histogram of the scanned image was measured to discover the levels of light and dark tones. This information will give us a reference point for subsequent inspections as the negatives get older and scanned images are transferred or migrated to other equipment.

As work was completed, the copy prints were made available to researchers, the negatives were moved to a temperature-and-humidity controlled vault and the original prints were put into acid-free envelopes and stored in another State Library facility.

CENTER POINTS OF THE 1934s

The latitude and longitude of the center of each photograph was identified by trying to find the same point on an online, geo-referenced U.S. Geological Survey topographic map. There were some difficulties with this process. For example, the Barkhamsted Reservoir did not exist in 1934. It is difficult to pin point the center of photographs of land that is now under water.

VIEWS TAKEN AFTER THE 1938 HURRICANE

The 132 oblique views of the damage that followed the September 1938 hurricane and flood were taken by the 118th Photographic Section of the U.S. Army Air Corps and the 43rd Division of the Connecticut National Guard presented the photographs to the Connecticut State Library. The photographs show flooding along the Connecticut River from Windsor to Wethersfield and in Cromwell, along Long Island Sound from East Haven to Narragansett, Rhode Island, along the Willimantic and Shetucket Rivers from Stafford to Norwich, and along the Quinebaug River in Putnam. The flights occurred on Sept. 23-24, 1938.

Oblique views are taken at an angle, which made it more difficult for us to determine the center point of each photograph. Sometimes, because the photographs were taken at low altitudes, it was possible to zoom in and identify buildings. However, the extensive flooding often obscures landmarks and the latitude and longitude that we provide should be considered merely an estimated center point.

The scene depicted is named on each photograph and this became the basis of the subject data. Often, it is possible to identify a specific building or business and this has been added to the description data when known. But, typically our data names only one town, even when more than one town is included in the view.

A number is inscribed on each photograph, like this: (0484-880E-118)(9-24-38-1P) (12-700). We believe that the first group of numbers relates to the 118th Photographic Section, the second group of numbers includes the date of the flight and the third group of numbers includes the altitude at which the photograph was taken, in this case 700 feet.

The original prints were scanned at 1200 dpi by John Lenehan of the State Library on a HP Scanjet 8300 scanner in Feb. 2007 and were converted to the JPEG2000 format for public display.

1965 AERIAL SURVEY OF CONNECTICUT

The Connecticut Public Works Department contracted with Keystone Aerial Surveys for a statewide survey in March and April 1965. There are 3,161 black and white photographs, from flight lines flown on an east to west axis. The original prints and index sheets are part of the Connecticut State Library, State Archives, RG 089, Records of the Department of Transportation.

SCANNING THE 1965 NEGATIVES

Staff of the Connecticut Department of Environmental Protection (DEP) and members of the public were using the photographs for research on such topics as historic sources of contamination and determination of permit requirements. Keystone, which had preserved the negatives in its vault since 1965, was hired by DEP in 2004 to scan the negatives. The specifications called for positive, grayscale images from the original negatives. The negatives were scanned at 15 microns, or 1693 dpi. The intent was to produce digital images as accurate as possible, so they could serve as a surrogate for the original photography.

CENTER POINTS OF THE 1965s

To enhance the use of the digital versions of the aerial photographs, DEP determined the approximate latitude and longitude for the upper left (northwest) corner location of each photograph. From that data, DEP calculated a point “approximately 5,000 feet to the right (east) and 5,800 feet down (south)” (p.9) in order to determine the coordinates of the center point. “Spot check comparisons of the resulting center point locations to the centers of the corresponding photo prints suggests they are positioned within 500 to 1,500 feet of their true location.” (p.9). For the State Library project, DEP converted the coordinates of the center points from NAD 1983 StatePlane Connecticut FIPS 0600 Feet to WGS84/NAD83 Latitude/Longitude in Decimal Degrees.

DEP asks researchers, when using the center point data, to “acknowledge the State of Connecticut, Department of Environmental Protection as the source for this information. For example, include the following data source description when printing this layer on a map: Aerial Photo Index – From the Connecticut 1965 Aerial Photo Center Point Index layer, compiled and published by CT DEP.” (p.2)

Regarding the center points, DEP states, “Although these data have been used by the State of Connecticut no warranty, expressed or implied, is made by the State of Connecticut as to the accuracy of the data and or related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the State of Connecticut in the use of these data or related materials. The user assumes the entire risk related to the use of these data. Once the data is distributed to the user, modifications made to the data by the user should be noted in the metadata.” (p.10)

(Quotations from “Connecticut 1965 Aerial Photo Center Point Index Personal GeoDatabase Feature Class – Photo_Index_1965, FGDC, ESRI Metadata”. This document was provided by Howie Sternberg, DEP, Mar. 1, 2007.)

ONLINE ACCESS TO THE AERIAL PHOTOGRAPHS

The effort to make the scanned images accessible over the internet involves converting the master files to the .jp2 (JPEG2000) format and importing them into the State Library’s image management software, called CONTENTdm. Users can search by town name and photograph number.

Since it is difficult to determine which photograph is the right one, researchers can navigate using series of maps. Starting with a statewide map, researchers can select a street map that shows the center points of the photographs. The street maps were constructed using the ArcView geographic information systems software from ESRI. The street maps can be searched to find specific street names of geographic features and then determine which photographs depict that area. Researchers can then enter the photograph number in the search box.

The Index Sheets created in 1934 have been scanned and will show a researcher which photograph illustrates a specific portion of the state.

It is hoped that we can make online access even easier in the future. Using geographic information systems software it is possible to add the latitude and longitude dots to interactive street maps or other kinds of online maps. This will allow researchers to click directly to the image of a photograph. Connecticut’s Aerial Surveys provides links and information on using the street maps and aerial photographs.