Science Verification Analysis and Calibration (SVAC) Plan 

Eduardo do Couto e Silva

Last update February 04, 2003

SVAC home

The SVAC Plan

The GLAST LAT SVAC Plan, is driven by the LAT Science Requirement Document and consists of pre and post-launch activities. The pre-launch activities are divided according to the available hardware at different phases of integration, whereas the post-launch activities consists of Phase 0 only, after which a working instrument is delivered to IOC.

• Instrument Calibrations – these ensure that the active elements of the LAT are spatially aligned and conversions from electronic signals and /or bit values into energy, position and time are within the required accuracy.  Instrument calibrations are divided into low and high level and they correspond to the basis of the first phase of post-launch calibrations.  As depicted in the diagram below these will be first performed under the I&T supervision and once it is demonstrated that the LAT is calibrated, the Instrument Operations Center (IOC) will take over the activities.

·     MC Validation – This activity, which is also part of the Beam Test Plan (LAT-TD-00444), is designed to verify with what accuracy the MC simulations reproduce the performance of the LAT.  As shown in the diagram below, instrument calibrations must be performed prior to final MC validation.

·     Verification of Science Requirements – Science Verification on the ground is done during the particle beam tests.  Measurements are performed at a limited, but well defined, number of points in the LAT parameter space (see Beam Test Plan LAT-TD-00444 for further details). The required accuracy for each of these measurements is specified in LAT-PS-00010-1.  Once validated, the MC simulations will then be used to estimate the performance of the LAT instrument at any point of the LAT parameter space. With a validated MC, the SAS group will produce the Instrument Response Functions.

Calibration data will be obtained from three hardware units

·         Engineering Model (EM) – single tower not fully instrumented

·        Calibration Unit (CU) – four-tower unit fully instrumented

·         LAT – sixteen-tower unit fully instrumented, flight hardware

The SVAC plan builds progressively on the knowledge acquired from testing single units and retesting after multiple towers have been assembled together. These hardware units are tested with either cosmic rays and/or particle beams. The next section outlines the focus of each hardware unit test.

One of the key elements of the calibration program is to perform data analysis for instrument calibrations and MC Verification. This is also discussed later in this note. The figure below shows the interdependence of the different parts of the program. Science Verification depends on information from both High and Low Level Calibrations and Software Performance tests. Prior to any test of the SVAC Plan we assume that the hardware has successfully passed the functional tests.