.. index:: Survey depth; Characterization, Relative photometric accuracy; Characterization .. _char-survey-relphot-accuracy: **CHAR-SURV-002:** Relative photometric accuracy ================================================ .. include:: definitions.rst Parent requirement ------------------ | `R-CAL-A-VS-4000 `_ | `R-CAL-A-NP-1000 `_ Cadence ------- Once, during PV phase. Objective --------- At the end of PV phase, we need to decide whether the survey can start as planned. Crucial parameters in this respect is whether the relative photometric accuracies can be achieved. We can estimate this from multiply detected sources in different images in the EDF-N and EDF-S passes during PV. Observations ------------ Methodology / Uplink procedure ------------------------------ :command:`Entity`: NISP, VIS :command:`Commanding Method`: None :command:`Dither Sequence`: ROS Targets and pointing constraints -------------------------------- Instrument configuration ------------------------ Inter-operability constraints ----------------------------- Dependencies ------------ Fulfilling ---------- Fulfilled by ------------ :ref:`calobs-block-pv-survey-validation` :ref:`calobs-block-f-wide-survey` Time-critical ------------- No Validation ---------- None. Recovery -------- None. In-orbit duration ----------------- Processing time --------------- Processing input ---------------- :command:`Ground Processing Input Data`: :command:`Data Description`: Data volume ----------- Processing tools ---------------- Standard wide-survey processing. Processing element ------------------ DataModel: ``_ Quality control parameters -------------------------- DataModel: ``_ Required accuracy, constraints ------------------------------ Processing method ----------------- Processing output ----------------- A single pass of the EDF-N consists of 43 ROS. These observations provide sufficient data to test top level requirements for the mission: **Relative photometric accuracy,** using multiple detections of the same source in two different categories: * in the overlap areas of adjacient fields. This focuses on sources when mapped at different detector areas, and is thus susceptive to residual large-scale illumination corrections errors, and other long-range effects. * in the group of four dithered exposures of the same field. This sample is not impacted by long-range effects. Ideally, there is no statistical difference between these two categories. Execute the following steps (or similar), for each of the four Euclid photometric bands, separately for each of the two categories mentioned above: 1. Obtain source photometry on individual, fully calibrated images. Retain only detections which did not have masked pixels within their measurement aperture. Specifically, reject detections whose flux could be biased by cosmics, persistence, crosstalk, hot or cold pixels, and similar. We have plenty of sources within a field, and plenty of overlap between adjacient fields, so we can choose to select very clean detections. 2. Identify all sources that have at least two valid detections. 3. Compute the mean source flux and the RMS for each multiply-detected object. 4. Define magnitude bins 0.5 mag wide (or smaller, if the statistics allows), starting with - and centered on - e.g. mag 18.0, and increase in steps of 0.5 mag. Compute the mean and the standard deviation of the RMS values of the multiple detections in each bin. Plot the mean RMS, and the standard deviation of the RMS as error bars, for each bin. 5. The bins centered on 24.0 AB mag (NISP) and 24.5 mag (VIS) are the reference bins. They should meet the top-level relative photometric requirements specified in the CalCD-A, specifically: R-CAL-A-NP-1000 (:math:`{\rm RMS}<1.5\%`) and R-CAL-A-VS-4000 (:math:`{\rm RMS}<1.0\%`). If the requirements are fulfilled, estimate a faint magnitude limit at which the requirements can no longer be met. Contact person -------------- Calibration Lead Status ------ |today| - In progress. FLAG ---- Priority -------- Observation record ------------------ Comments -------- .. raw:: latex \clearpage