Document: m99_cals.txt (written: 18th Jan, 2000)

See the document m99_IOPreadme.txt for more information on the 
measurements made with the SlowDROP platform.  The cruise 
report and station logbook contain further details and 
descriptions of the work done (m99_cruise_report.htm and 
m99_metalog.htm).

MOCE-5 - Instrument Calibration Files

The following calibration files were used and have been 
submitted to SeaBASS:

CTD		modis_p128.con, modis_p242.con
HydroScat	HS990317 26mar99-corrected.ini
ac90141		ac90141_05-17-99.dev
ac90196		ac90196_08-23-99.dev
ac90123		ac90123_09-16-99.dev

NB The CTD configuration file modis_p128 was only used for 
casts 01p_001 to 06c_001. Different files arose from using 
different pressure sensors.


MOCE-5 - ac-9 Calibration Issues

SLOWDROP Profiling System

	There were two ac-9's on the SLOWDROP instrument 
platform ac90141 and ac90196.  At least one profile was made 
with the SlowDROP at each station.  The following format was 
used for file naming : m991006c_003.ext.  Where m99 = cruise 
ID, 10 = month, 06 = day in October, c = cast type (c-
calibration, v-validation, p-process), 003 = cast number and 
ext = file extension.  Cast type was dictated by when in the 
schedule of all cruise operations the SlowDROP profile was 
performed.  Validation casts were the first over-the-side 
operation for each station and generally took place within four 
hours before the satellite overpass.  Process and calibration 
casts were slotted into the schedule whenever time and 
conditions allowed.  In these SeaBASS documents, specific casts 
are referred to by day, type and number for example 06c_003. 

	Generally one ac-9 was run unfiltered in order to 
measure totals and one ac-9 had a 0.2 micron filter attached to
the attenuation or absorption flow tube, to measure the 
dissolved component.  For five casts this configuration was 
changed and both instruments were run either both filtered 
(06c_001, 09p_001 and 12c_001) or both unfiltered (01p_001 and 
20p_001) in order to make inter-instrument comparisons and 
assist in the diagnostic process.  
	
	The ac-9's had their factory calibration offsets 
applied via their respective device files.  However to keep 
track of and account for instrument drift, field calibrations 
were made, on average, once a day during the cruise.
		
	Field calibrations used a clean water standard produced
by a Barnstead Nanopure water system.  Each absorption and 
attenuation side was calibrated separately and at least once 
during each calibration session.  A total of eighty calibration 
files were taken, in a total of sixteen calibration sessions.  
Individual calibration files are referred to by a session number 
and sequential letter, for example 2c indicates the third file 
taken during the second calibration session of the cruise.  The 
data within each calibration file was averaged in order to 
obtain a single offset for each wavelength for that calibration. 

INLINE AC-9 SYSTEM

	Dr. Dennis Clark's ac-9 (ac90123) was used to measure 
the spectral absorption and beam attenuation properties 
continuously along the ship's track.  Surface water was obtained
from the ships intake (located approximately at 5m water depth) 
and provided a continuous flow of surface water to the ac-9.  
The meter was placed in a modified freezer to maintain the 
external temperature of the ac-9 a roughly a constant 
temperature.  We tried to keep the freezer temperature within 5 
degrees of the surface ocean temperature in order to reduce the 
effects of large thermal gradients on the ac-9.  The data was 
collected through the WET Labs provided WETView software, which 
averaged the data (6Hz) over 16.7 seconds.  The inline ac-9 data
was then merged with the 1 minute resolution ships metadata and 
the ships thermosalinograph data using a nearest neighbor 
scheme.  Data collection began on October 2.  However, it took 
a while to effectively stabilize the inline feed into the ac-9 
system so that bubbles were not a problem in the data stream.  
As is such, the first useable data began on October 5 lasting 
until October 21.

	The meter was calibrated at WET Labs 2 weeks before the 
start of the cruise (9/16/99), and the device offsets were using
in processing the data (ac90123_09-16-99.dev).  Field 
calibrations were performed as described above with the 
exception that the absorption and attenuation sides were 
calibrated simultaneously.  The calibration offsets used are 
described below.


AC9 OFFSETS

AC90196 attenuation calibrations
	In order to provide field calibration offsets applicable
to each day of the cruise, the full set of field calibrations 
was processed in the following manner.  For any day that had 
more than one calibration file, the offsets from each 
calibration were averaged for each wavelength.  For any day(s) 
without a calibration file, the calibration offsets were linearly 
interpolated between the two nearest calibration times.  This 
series of offsets were then smoothed using a 3 point running 
mean, providing a set of offsets for each day.

AC90196 absorption calibrations
	A set of offsets was obtained in the same manner as for 
the absorption measurements.  The full set of offsets is given 
at the end of this document.

AC90141 
	The device file for this instrument was found to contain 
erroneous internal temperature correction data. Hence all the
absorption data from ac90141 may be considered questionable as 
it contained inaccuracies in magnitude and also showed some 
pressure dependence.  Some of this was corrected by incorporating 
corrected calibration offsets.

AC90141 absorption calibrations
	A series of offsets was obtained in the same manner as 
for ac90196 giving one set per day (if more than one calibration 
per day, they are averaged, missing days are interpolated). With
the following two exceptions:  all casts on days 4,5,6 and casts 
16v_003, 17v_001 and 17p_001.
	For the period day 4-6, vicarious offsets were determined
from the calibration sessions 2 and 5, and by comparison of data 
from the inter-calibraton casts at 04c_001, 06c_001 and 
09p__001.  For the second period offsets were derived from the 
calibration sessions 12, 13, and 14.

AC90141 attenuation calibrations
	A set of offsets was obtained in the same manner as for 
the attenuation measurements of ac90196.  The full set of offsets is given 
at the end of this document.

AC90123 absorption calibrations
	The absorption side of the meter showed an inversion 
response, whereby the shape of the absorption calibration 
offsets became inverted twice during the deployment.  The 
transition from the normal to inverted state and back to the 
normal state typically took one day.  As is such, it was 
necessary to create a time series of the absorption offsets to 
correct for this effect.  Using the field calibrations and the 
comparisons to the profiler ac-9 data, we fit offset functions 
based on time.  Shown at the end of this document is the hinge 
points of these calibration offset functions for each of the 
wavelengths.  At periods inbetween the hinge points, the offset 
data was fit to a one minute resolution time series using a 
linear fit based on the two nearest calibration offset hinge 
points.

AC90123 attenuation calibrations
	The attenuation side of ac90123 did not show the 
inversion effect observed on the absorption side of the meter.  
Furthermore, the field calibration offsets were sufficiently 
close to one another to merit using an average set of 
calibration offsets for each of the wavelengths.  These average 
offsets are shown at the end of this document. 


DATA PROCESSING 

SLOWDROP Profiler Data

	It should be noted that the dissolved component was 
sometimes measured with the attenuation side of an ac-9 but 
for the dissolved fraction, attenuation is assumed to be 
equal to absorption.

Several corrections were applied to the data set: 

-The dissolved data was lagged by 24 scans (approximately 4 
seconds) to compensate for filter effects. 

-Temperature and salinity corrections were made, using a 
calibration temperature of 26.0 degrees celsius.

-The scattering correction method used in computing the total 
absorption was to subtract the apg715 data from each 
wavelength. 

-The ays data was also smoothed using a 9 second window.

Some additional processing was required to correct for specific 
instrument errors or problems:

- all data: first binned to 25cm in order to reduce the
noise in the data caused by ship motion translated through the 
winch wire. 

- ac90141 filtered measurements: The absorption data had 
incorrect internal temperature compensation hence the 
attenuation side was used to measure the dissolved component 
when that meter was filtered.  However the attenuation side 
showed some depth dependence and therefore c715 was subtracted 
from all wavelengths to compensate.

- ac90141 measuring totals: The absorption measurements also 
showed some depth dependence, which was corrected by subtracting 
a715 from all wavelengths, ie this was the scattering correction 
method used.

- ac90196 filtered measurements: The absorption data had to be 
smoothed in order to correct for a ground loop problem which 
induced a noise level of +- 0.005.  In order to keep consistency 
in the dissolved absorption data set, the 715 nm channel was 
also subtracted from the other wavelengths measuring the 
dissolved absorption on ac90196.

INLINE AC9 Data

-The absorption and attenuation measurements were corrected
for the temperature and salinity dependence of water using
the one minute averaged output of the ship's thermosalinograph.
The absorption data was further corrected for scattering 
errors by subtracting the 715 nm absorption channel from
all other wavelengths.


REFERENCES
Pegau, W.S., D. Gray, and J.R.V. Zaneveld.  "Absorption of 
visible and near-infrared light in water: The dependence on 
temperature and salinity".  Appl. Opt., 36,6035-6046, 1997.
M.L. Twardowski et al.  "Quantification of the micro- to 
finescale in situ chromophoric DOM absorption and total 
absorption in coastal waters with an ac-9". Journal of Atmos. 
And Ocean. Tech. Submitted. 1997
Ac-9 protocol available to download at: 
ftp://wetlabs.com/pub/ac9/AC9PROTU.TXT

ac90196 absorption offsets
date	a412	a440	a488	a510	a532	a555	a650	a676	a715
1	0.0521	0.0221	-0.0009	-0.0020	-0.0046	-0.0065	-0.0114	-0.0153	-0.0109
2	0.0502	0.0197	-0.0034	-0.0048	-0.0066	-0.0091	-0.0138	-0.0182	-0.0130
3	0.0547	0.0240	0.0018	-0.0003	-0.0036	-0.0060	-0.0108	-0.0137	-0.0107
4	0.0541	0.0212	-0.0038	-0.0054	-0.0071	-0.0101	-0.0152	-0.0203	-0.0146
5	0.0600	0.0250	-0.0016	-0.0033	-0.0056	-0.0085	-0.0142	-0.0195	-0.0141
6	0.0610	0.0241	-0.0038	-0.0053	-0.0070	-0.0103	-0.0158	-0.0220	-0.0154
7	0.0620	0.0233	-0.0060	-0.0073	-0.0084	-0.0120	-0.0173	-0.0246	-0.0167
8	0.0617	0.0238	-0.0037	-0.0057	-0.0067	-0.0104	-0.0159	-0.0224	-0.0149
9	0.0615	0.0229	-0.0047	-0.0065	-0.0077	-0.0116	-0.0165	-0.0236	-0.0155
10	0.0630	0.0253	-0.0008	-0.0033	-0.0047	-0.0086	-0.0135	-0.0194	-0.0124
11	0.0687	0.0284	0.0000	-0.0028	-0.0049	-0.0090	-0.0140	-0.0198	-0.0125
12	0.0697	0.0295	0.0017	-0.0010	-0.0035	-0.0074	-0.0126	-0.0181	-0.0111
13	0.0749	0.0328	0.0037	0.0006	-0.0026	-0.0065	-0.0126	-0.0175	-0.0106
14	0.0751	0.0324	0.0026	-0.0003	-0.0034	-0.0073	-0.0137	-0.0193	-0.0122
15	0.0752	0.0319	0.0015	-0.0012	-0.0043	-0.0081	-0.0149	-0.0211	-0.0137
16	0.0765	0.0323	0.0009	-0.0017	-0.0049	-0.0088	-0.0156	-0.0222	-0.0146
17	0.0777	0.0327	0.0003	-0.0022	-0.0055	-0.0095	-0.0163	-0.0233	-0.0156
18	0.0806	0.0347	0.0019	-0.0008	-0.0045	-0.0087	-0.0157	-0.0223	-0.0152
19	0.0820	0.0357	0.0027	-0.0001	-0.0040	-0.0083	-0.0155	-0.0218	-0.0150
20	0.0834	0.0367	0.0034	0.0006	-0.0035	-0.0078	-0.0152	-0.0214	-0.0147

ac90196 attenuation offsets
date	c412	c440	c488	c510	c532	c555	c650	c676	c715
1	0.0074	0.0121	0.0121	0.0135	0.0116	0.0122	0.0049	0.0004	0.0060
2	0.0063	0.0108	0.0107	0.0124	0.0102	0.0114	0.0041	-0.0002	0.0063
3	0.0052	0.0095	0.0094	0.0113	0.0087	0.0105	0.0033	-0.0008	0.0066
4	0.0050	0.0090	0.0085	0.0111	0.0076	0.0086	0.0022	-0.0021	0.0067
5	0.0047	0.0084	0.0075	0.0110	0.0064	0.0067	0.0012	-0.0035	0.0067
6	0.0037	0.0083	0.0082	0.0116	0.0070	0.0069	0.0013	-0.0036	0.0065
7	0.0028	0.0081	0.0088	0.0122	0.0075	0.0071	0.0015	-0.0037	0.0063
8	0.0021	0.0091	0.0108	0.0133	0.0092	0.0085	0.0021	-0.0032	0.0057
9	0.0006	0.0085	0.0112	0.0137	0.0097	0.0090	0.0025	-0.0033	0.0056
10	0.0003	0.0099	0.0119	0.0149	0.0109	0.0090	0.0035	-0.0017	0.0065
11	-0.0009	0.0098	0.0127	0.0146	0.0116	0.0102	0.0038	-0.0011	0.0078
12	-0.0011	0.0103	0.0123	0.0154	0.0123	0.0097	0.0052	0.0010	0.0090
13	-0.0014	0.0110	0.0137	0.0154	0.0137	0.0113	0.0062	0.0026	0.0100
14	-0.0010	0.0111	0.0134	0.0155	0.0139	0.0107	0.0068	0.0034	0.0098
15	-0.0006	0.0113	0.0130	0.0156	0.0140	0.0100	0.0074	0.0042	0.0096
16	-0.0001	0.0115	0.0127	0.0156	0.0142	0.0094	0.0080	0.0051	0.0094
17	0.0003	0.0116	0.0124	0.0157	0.0144	0.0088	0.0086	0.0059	0.0093
18	0.0007	0.0118	0.0121	0.0157	0.0146	0.0082	0.0091	0.0068	0.0091
19	0.0009	0.0119	0.0119	0.0157	0.0147	0.0079	0.0094	0.0072	0.0090
20	0.0012	0.0119	0.0118	0.0158	0.0148	0.0076	0.0097	0.0076	0.0089

ac90141 absorption offsets
date	a412	a440	a488	a510	a532	a555	a650	a676	a715
1	-0.0017	-0.0019	-0.0060	-0.0003	-0.0019	-0.0056	-0.0041	-0.0049	-0.0171
2	-0.0017	-0.0019	-0.0060	-0.0003	-0.0019	-0.0056	-0.0041	-0.0049	-0.0171
3	-0.0017	-0.0019	-0.0060	-0.0003	-0.0019	-0.0056	-0.0041	-0.0049	-0.0171
4	-0.0122	-0.0106	-0.0140	-0.0084	-0.0098	-0.0129	-0.0126	-0.0131	-0.0219
5	-0.0227	-0.0192	-0.0220	-0.0166	-0.0177	-0.0202	-0.0211	-0.0212	-0.0267
6	-0.0379	-0.0325	-0.0343	-0.0291	-0.0302	-0.0319	-0.0341	-0.0342	-0.0334
7	-0.0530	-0.0457	-0.0467	-0.0416	-0.0426	-0.0435	-0.0472	-0.0471	-0.0402
8	-0.0477	-0.0430	-0.0442	-0.0399	-0.0406	-0.0423	-0.0459	-0.0455	-0.0384
9	-0.0557	-0.0494	-0.0494	-0.0462	-0.0469	-0.0481	-0.0523	-0.0520	-0.0417
10	-0.0407	-0.0388	-0.0415	-0.0370	-0.0372	-0.0396	-0.0431	-0.0426	-0.0370
11	-0.0404	-0.0365	-0.0372	-0.0352	-0.0353	-0.0375	-0.0414	-0.0408	-0.0329
12	-0.0323	-0.0304	-0.0337	-0.0293	-0.0294	-0.0319	-0.0350	-0.0346	-0.0315
13	-0.0254	-0.0235	-0.0262	-0.0228	-0.0229	-0.0256	-0.0282	-0.0281	-0.0257
14	-0.0288	-0.0265	-0.0291	-0.0257	-0.0259	-0.0283	-0.0310	-0.0307	-0.0299
15	-0.0323	-0.0296	-0.0320	-0.0287	-0.0288	-0.0310	-0.0338	-0.0334	-0.0340
16	-0.0333	-0.0303	-0.0326	-0.0293	-0.0296	-0.0317	-0.0344	-0.0340	-0.0347
17	-0.0343	-0.0309	-0.0332	-0.0300	-0.0303	-0.0324	-0.0351	-0.0346	-0.0355
18	-0.0230	-0.0207	-0.0236	-0.0199	-0.0203	-0.0228	-0.0244	-0.0245	-0.0280
19	-0.0166	-0.0146	-0.0173	-0.0134	-0.0143	-0.0167	-0.0175	-0.0177	-0.0253
20	-0.0102	-0.0086	-0.0110	-0.0070	-0.0083	-0.0106	-0.0105	-0.0109	-0.0225

ac90141 attenuation offsets
date	c412	c440	c488	c510	c532	c555	c650	c676	c715
1	0.0252	0.0232	0.0224	0.0199	0.0239	0.0232	0.0189	0.0179	0.0148
2	0.0180	0.0167	0.0149	0.0123	0.0161	0.0156	0.0115	0.0098	0.0067
3	0.0138	0.0129	0.0105	0.0079	0.0117	0.0112	0.0074	0.0052	0.0022
4	0.0127	0.0119	0.0092	0.0068	0.0105	0.0098	0.0066	0.0040	0.0011
5	0.0115	0.0109	0.0079	0.0057	0.0094	0.0084	0.0058	0.0028	0.0001
6	0.0107	0.0101	0.0072	0.0050	0.0088	0.0075	0.0055	0.0020	-0.0006
7	0.0101	0.0095	0.0070	0.0048	0.0085	0.0071	0.0058	0.0016	-0.0008
8	0.0086	0.0088	0.0071	0.0049	0.0084	0.0069	0.0056	0.0014	-0.0013
9	0.0073	0.0083	0.0070	0.0046	0.0083	0.0066	0.0051	0.0011	-0.0019
10	0.0086	0.0100	0.0081	0.0056	0.0090	0.0076	0.0049	0.0017	-0.0020
11	0.0105	0.0117	0.0090	0.0068	0.0098	0.0083	0.0047	0.0019	-0.0019
12	0.0127	0.0137	0.0103	0.0084	0.0106	0.0095	0.0048	0.0023	-0.0017
13	0.0126	0.0139	0.0105	0.0088	0.0107	0.0094	0.0048	0.0020	-0.0020
14	0.0135	0.0147	0.0112	0.0093	0.0111	0.0099	0.0057	0.0026	-0.0017
15	0.0143	0.0156	0.0120	0.0097	0.0115	0.0105	0.0067	0.0031	-0.0014
16	0.0150	0.0162	0.0130	0.0103	0.0124	0.0113	0.0078	0.0039	-0.0007
17	0.0156	0.0166	0.0143	0.0111	0.0138	0.0122	0.0090	0.0049	0.0002
18	0.0160	0.0168	0.0159	0.0120	0.0158	0.0134	0.0104	0.0062	0.0015
19	0.0173	0.0175	0.0172	0.0128	0.0174	0.0147	0.0116	0.0075	0.0023
20	0.0196	0.0186	0.0181	0.0134	0.0189	0.0161	0.0127	0.0089	0.0026


ac90123 absorption offsets
date		a412	a440	a488	a532	a555	a630	a650	a676
10/5 	01:50	0.03364	0.016558	0.00036	-0.00001	-0.0017	-0.0007	-0.0023	-0.0037
10/9	14:17	0.06239	0.0318	0.0015	-0.0067	-0.0059	-0.0007	-0.0023	-0.0037
10/12	05:05	-0.08011	-0.0501	-0.0324	-0.0229	-0.0179	-0.01088	-0.0085	-0.0083
10/12	06:57	0.0	-0.0035	-0.012	-0.0122	-0.01	-0.0052	-0.0063	-0.0062
10/12	11:09	0.08113	0.0432	0.0084	-0.0018	-0.002	0.00136	-0.0041	-0.0037
10/15	02:40	0.08113	0.0432	0.0084	-0.0018	-0.002	0.00136	-0.0041	-0.0037
10/16	21:31	0.02582	0.006	-0.00884	-0.0129	-0.0085	-0.0071	-0.0084	-0.0086
10/18	16:50	0.00778	0.0033	-0.0055	-0.0091	-0.0078	-0.0066	-0.0062	-0.0064
10/19	23:59	-0.05634	-0.0325	-0.0177	-0.01503	-0.0098	-0.007	-0.0063	-0.01026
10/20	18:42	0.08493	0.0472	0.01396	0.0018	-0.00045	0.0018	-0.0037	-0.0044
10/21	14:15	0.08493	0.0472	0.01396	0.0018	-0.00045	0.0018	-0.0037	-0.0044

ac90123 attenuation offsets
date 	c412	c440	c488	c532	c555	c630	c650	c676
10/1 - 10/21	-0.001	0.0069	0.0095	0.0064	0.0087	-0.0106	0.0066	0.0046
