Last Updated Jan 2001

Copyright © 2001 The Association of Universities for Research in Astronomy, Inc. All Rights Reserved.

INTRODUCTION:

At this point scanning, processing, and archiving production capabilities are adequately established. An equally important consideration is quality assurance of the products. The goal is to prevent or immediately correct production errors or poor data quality.

Several guiding principles are assumed in the specific plans described below:

• open communication concerning both normal operations and problems;
• thorough understanding of processes and data;
• appropriate diagnostic measures and tools for determining quality;
• independent checks of quality; proper inspection and maintenance to prevent problems.

PLATES:

Observatory liason

Northern hemisphere plates are taken at the Oschin Schmidt Telescope and the original plates of the POSS-II J, R, and N surveys are loaned to us by the Palomar Observatory. Southern hemisphere plates are taken with the UK Schmidt and generally distributed by the Royal Observatory, Edinburgh. STScI is purchasing copy plates of the SERC-ER (Equatorial R) Atlas. ROE loans original plates of the AAO-R survey to STScI.

Scheduling deliveries to and from STScI requires a high level of vigilance and timely communication (usually e-mail or telephone) with observatory staff.

CASB sends requests in a timely fashion to the observatories for additional shipments when stocks of unscanned plates run low. Likewise, observatories may need expedited return shipments on timescales of weeks to months.

Observatories communicate shipment lists via e-mail before actual shipments are shipped. The records in these formatted files contain observing data (field, bandpass, epoch, exposure time, etc.) for each plate. This allows QA of the shipments including:

• db search for duplicates to prevent observatory shipments from containing plates which have already been at STScI;
• prioritization of fields to provide QA of whether proposed shipment follows agreed upon science priorities in terms of fields and bandpasses;
• queries about location of plates.
• tracking shipments

Most shipments contain irreplaceable plates. Therefore careful tacking is performed to prevent loss. This tracking includes:

• acknowledgement of shipment receipts

  E-mail acknowledgements are sent ASAP upon the arrival of all shipments either at the observatories or at STScI.

• QA of shipping procedures

  The liaison person documents instructions to STScI shipping staff for outbound shipments and checks to ensure that the instructions are followed. These instructions include strapping the shipping containers and insurance provisions.

The liaison person collects all shipping documents as shipments are received from ROE and transmits copies of these documents to ROE to prevent customs problems when the shipments are returned. When necessary, the liaison person communicates directly with STScI's customs broker.

Plate handling:

These survey plates are 14 inches (355 mm) square. The fragile original plates are 1 mm thick while the heavier copy plates are 3mm thick. Special training is required for handling these plates to ensure that neither the plate nor the operator is injured. Care must be taken to protect the plate emulsion and glass surfaces. Approved procedures must be followed for unpacking/packing, storing, display, and mounting plates on the microdensitometers.

Experienced plate handlers explain the concepts and demonstrate the techniques to new staff members. New staff practice with unusable plates. The instructor is responsible for certifying the new plate handler. No one is allowed to handle survey plates alone until he/she is certified.

The plates, in individual Tyvek envelopes are tightly packed in one or more Kodak boxes inside padded shipping containers. The plate boxes are unloaded from or loaded into the containers outside the plate vault to avoid dust contamination in this clean room. For safety reasons and to aid in emergencies two staff members must be present in the plate vault during packing or unpacking of the Kodak boxes. One person slides each plate out of its envelope to check its condition and identification, replaces the plate in the envelope, and either shelves the (incoming) plate or places it in the outgoing box. The second person checks the plate off the shipping list and notes discrepancies or abnormal plate condition. The annotated shipping list is returned to the liaison who is responsible for reporting the information to the observatory.

Damaged plates are immediately reported to the observatory liaison. Discovery of damaged or broken plates can be stressful. Usually the packing/unpacking operation is suspended following such events.

CASB has a supply of Tyvek envelopes for use in re-enveloping the plates; however, the following caveats apply to this procedure:

• Envelopes are never changed for second-generation plates;
• ROE insists on the return of their plates in the original envelopes; therefore, ROE envelopes MUST be saved if ROE plates are ever re-enveloped.

Plate handling techniques are described in SO-04, Guide Star Selection System Volume 5: Operators; Manual. This documentation should be updated for the current environment.

[General rules are documented in pipe_help, an on-line help library.]

Films and Prints:

STScI also acquires some film and print copies of the survey plates. These media also can be easily damaged. They are in some ways more fragile than glass. Handling must be minimized until procedures for their use are established.

Storage:

Plates, films, and prints are stored in cabinets in the plate vault. Plates are stored vertically in individual envelopes. Prints are stored horizontally in books. Films were originally stored horizontally in individual casings. For better preservation they are being trans- ferred to a new cabinet where they hang vertically from specially designed rods and attachments. The permanent plate collections are stored by field for each survey. Plates on loan are stored by field and survey in areas reserved for for non-scanned and scanned plates. CASB makes limited spaces available for plates owned by or loaned to other STScI astronomers. Each plate cabinet is clearly labeled with its contents.

Internal plate tracking:

If errors, including additional or missing plates, are found during unpacking, the liaison reports such discrepancies to the observatories. and requests corrected observing records from them. The liaison then corrects any erroneous records in the shipping list which then is read by a utility program to enter the attributes of the plates into the database, generate data files for future scanning and processing, and set the database in-house flag. These procedures ensure that the data in the local database agree with that in the observatory databases.

The liaison enters a summary record into the flat file listing all plate and tape shipments and also archives the shipping list.

Another utility program is then run to generate a file used by the CNS staff to print tape and folder labels. These labels are printed in the order in which plates are to be scanned and help to prevent the scanning of wrong plates.

A logout utility program is used to read each outbound shipping list and resets the database in-house flag for each plate in the shipment.