GALFA Error Flags

September 23, 2004
Jeff Mock

The G_ERR column is an unsigned short int (16-bits). By some FITS convention, 16-bit unsigned numbers are stored with an offset of -32768. So, you need to add 32768 to G_ERR to get the right value. If you look at the file with "fv", fv adds the correct offset form the file header. So, when there is no error condition G_ERR should have a value of 0 (-32768 stored in the file).

The following bit description is from the source code in cl/src/diag/gfits.c:

For each beam, there are overflow conditions. Two bits indicate errors of various degrees:

0 0-15 errors in previous 1s
1 16-255 errors in previous 1s
2 256-4095 errors in previous 1s
3 >=4096 errors in previous 1s

err = (g[0]->misc >> 16) & 0xffff

err[1:0] wideband up shift saturation
err[3:2] wideband FFT overflow
err[5:4] narrowband up shift saturation
err[7:6] narrowband FFT overflow
err[9:8] narrowband lowpass filter saturation
err[11:10] narrowband mixer saturation