From 2064e73aa634954a5369ebe02862e23b1e070768 Mon Sep 17 00:00:00 2001 From: "M. Teodoro" Date: Mon, 30 Dec 2024 15:04:30 -0500 Subject: [PATCH] Add description of calculation of VAR_SKY. --- docs/roman/resample/arguments.rst | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/docs/roman/resample/arguments.rst b/docs/roman/resample/arguments.rst index 78bcf3b49..668ef208d 100644 --- a/docs/roman/resample/arguments.rst +++ b/docs/roman/resample/arguments.rst @@ -77,14 +77,20 @@ image. The weighting type for each input image. If `weight_type=ivm` (the default), the scaling value will be determined per-pixel using the inverse of the read noise - (VAR_RNOISE) array stored in each input image. If the VAR_RNOISE array does + (``VAR_RNOISE``) array stored in each input image. If the ``VAR_RNOISE`` array does not exist, the weight is set to 1 for all pixels (equal weighting). If `weight_type=exptime`, the scaling value will be set equal to the exposure time found in the image header. If `weight_type=ivsky`, the scaling value will be determined per-pixel - using the inverse of the sky variance (VAR_SKY) array calculated in the - resample step for each input image. If the VAR_SKY array does - not exist, the weight is set to 1 for all pixels (equal weighting). + using the inverse of the sky variance (``VAR_SKY``) array calculated in the + resample step for each input image. ``VAR_SKY`` is given by the following equation: + + .. math:: + + \text{VAR\_SKY} = \text{VAR\_RNOISE} + \text{VAR\_POISSON} \, \frac{ med(\text{DATA}) }{ \text{DATA} }, + + where :math:`\text{DATA}` and :math:`med(\text{DATA})` correspond to the data array and its median, respectively. + If the ``VAR_SKY`` array does not exist, the weight is set to 1 for all pixels (equal weighting). ``--single`` (bool, default=False) If set to `True`, resample each input image into a separate output. If