PDS_VERSION_ID = PDS3
RECORD_TYPE = STREAM
DATA_SET_ID = "RO-A/CAL-ALICE-4-AST2-V1.0"
PRODUCT_CREATION_TIME = 2010-03-26T19:10:00
PRODUCT_ID = "ALICE_DATA_TO_RAYLEIGHS"
OBJECT = TEXT
INTERCHANGE_FORMAT = ASCII
PUBLICATION_DATE = 2010-04-01
NOTE = "Description of the how to convert calibrated Alice
data (CODMAC level 3 or 4) data from the default flux units to units of
Rayleighs per Angstrom."
END_OBJECT = TEXT
END
The primary data extension of CODMAC level 3 Rosetta Alice data (SCI) is in
flux units (photons cm^-2 s^-1). To convert to differential flux units, it is
neccesary to first divde the image by the dispersion for each pixel. This is
approximately 1.73 Angstroms/pixel, however it varies across the detector. The
following IDL code illustrates how this could be done:
IDL> rdfits_struct, SCI_filename, data
IDL> dlambda = data.im2 - shift(data.im2, -1)
IDL> dlambda[1023,*] = dlambda[1022, *]
IDL> data.im0 /= dlambda
In the above example, data.im0 will now be in units of photons cm^-2 s^-1
Angstrom^-1. Linearized Alice data (LIN) are already in these units.
To convert from photons cm^-2 s^-1 Angstrom^-1 to Rayleighs per Angstrom
(10^6/4 Pi photons cm^-2 s^-1 sr^-1 A^-1) it is necessary to multiply each
pixel by 4 Pi/10^6. Finally the pixels in each row of the detector must be
divided by the solid angle subtended by the source. In the case of a uniformly
illuminated slit, this solid angle is that subtended by that detector
row. Rows subtend approximately 0.30 degrees in the spatial direction and
between 0.05 and 0.10 degrees in the spectra dimension. The following list
gives the solid angle (in units of steradians) subtended by each row as a
function of row number (zero-indexed):
Row Number Solid Angle
0 NaN
1 NaN
2 NaN
3 NaN
4 NaN
5 9.38222e-06
6 9.38222e-06
7 9.38222e-06
8 9.38222e-06
9 9.38222e-06
10 9.38222e-06
11 9.38222e-06
12 7.03666e-06
13 4.69111e-06
14 4.69111e-06
15 4.69111e-06
16 4.69111e-06
17 4.69111e-06
18 4.69111e-06
19 9.38222e-06
20 9.38222e-06
21 9.38222e-06
22 9.38222e-06
23 9.38222e-06
24 NaN
25 NaN
26 NaN
27 NaN
28 NaN
29 NaN
30 NaN
31 NaN