NEAR/MSSS Calibration Home Page

This document will list the most recent report nearest the top of the page.

NOTE: If any of you find mistakes or errors or omission or comission, please let me know so I can correct these in future reports.

NEAR MSI Hyakutake Images (authored by Mark Robinson, Last Updated: 4/4/96)

Mark presents a first look at the Hyakutake images. Included on this page is a single dark corrected, coma centered image along with a "contact sheet" of thumbnail images for the entire sequence. Also included on this page is a table put together by Jeff Warren (MSSS) to correlate the FITS image names with the planning sequence table included on Cornell's Hyakutake observation page.

NEAR MSI Lunar Images (authored by Mark Robinson, Last Updated: 2/23/96)

Mark presents his on-going analysis of MSI lunar images taken shortly after launch for system calibration purposes. He provides statistical summaries of pixel intensities for raw images, darks and flats, and images that have been dark-, smear- and flat-corrected. No calibrated image analysis is yet available. An unexpected feature of some images is moon reflections, perhaps from the optics cover. These are most prominent in long exposure frames.

NIS Sample Measurements "On-line" (authored by Jim Bell and Andy Switala, 11/07/95) - Note: this file is on Jim's machine at Cornell.

Jim and Andy have put the spectra for the rock material samples measured in the Optical Calibration Facility, appropriately calibrated for dark current and spectral cross-talk, on-line. The spectra come in two flavors: identified and unidentified. Those of you interested in attempting to identify the samples "blind" should look at the latter first.

Locations of Instrument Footprints in the MSI Field of View (authored by Scott Murchie and Ed Hawkins, 10/18/95)

Scott and Ed have worked out the locations of the NIS and NLR FOVs in the MSI frame, in MSI pixel coordinates as viewed on a video monitor. This memorandum provides this information

Preliminary Comparison of NIS and MSI Spectra of Samples (authored by Jim Bell, Andy Switala, and Mark Robinson, 10/18/95) - Note: this file is on Jim's machine at Cornell.

Jim and Andy have combined their initial reduction of the NIS data with Mark's work on the MSI data (see below) or click here. They note that the MSI and NIS spectra match up remarkably well in the spectral overlap region. Since they have applied no scaling or other massaging processing to these data, they conclude that the nice overlap reflects the inherent quality of the data (a testimony to the intrinsic capability of the instruments) and our opportunity to measure the same samples in essentially the same setup.

MSI Spectra of Samples (processed and written by Mark Robinson, 10/11/95

Mark sent the NEAR MSI/NIS team an e-message (reproduced at the beginning of this file) describing his processing of MSI data to extract spectra of the rock and powder samples imaged in May. Mark's graphs have been coverted from postscript to gif format and are included in this file.

MSI Dark Field Data ( written by Mark Robinson, 8/27/95

Mark reports on his initial look at dark field data. Among his findings are:

1. There is an odd/even offset of sample values of roughly 5 DN.
   
2. There is as much as 10 DN of "microphonic," periodic noise, which is attributed to support electronics. However, Mark indicates Scott is looking to make sure it is not in the instrument.
   

Mark also includes a "notebook" of things he observed during his examination of the images.

Leakage of unblocked second-order signal onto Ge detector (written by Jim Bell and Andy Switala, 7/13/95)) - Note: this file is on Jim's machine at Cornell

Second-order light leakage is going to be a serious concern in NEAR data. The effect will be noticed in Ge detector channels 1 through 5, (centered on 818 to 905 nm). For example, fully 30% of whatever flux detected from Eros at 1700 nm will be transmitted through the order-sorting filter onto the Ge detector as 850 nm light, and this component will be added on top of whatever flux seen from Eros at 850 nm proper. The effect reachs a maximum of about 60% in Ge channel 1. This leakage occurs in a critical spectral region, as it is the short-wavelength end of the 1-micron pyroxene feature, and also includes the overlap region with the MSI camera filters. However, Jim feels there is nothing to preclude easy correction for this second-order leakage, provided adequate calibration data. Jim recommends that during the present OCF run: (1) the monochrometer be stepped through at finer sampling to better characterize the leakage curve, and (2) the limits of the monochrometer scan be set at 1550 to 1900 nm, so that the leakage curve can be characterized over and slightly beyond the entire responsive spectral range of Ge channels 1 through 6.

Detector noise induced by holding the NIS slit in closed position (written by Jim Bell and Andy Switala, 7/13/95)) - Note: this file is on Jim's machine at Cornell

It does not appear that the motor that holds the shutter in the closed position adds any statistically significant noise to either the Ge or InGaAs detectors. The increased standard deviation of the dark signals at the longer wavelengths in each detector are most likely a result of lower SNR in those elements. Jim and Andy recommend that a few additional OCF tests be performed, if time allows, to examine the possibility that a small amount of light is leaking beyond the closed shutter onto the Ge detector.

Better wavelength calibration of Ge and InGaAs detec tors (written by Jim Bell and Andy Switala, 7/13/95)) - Note: this file is on Jim's machine at Cornell

Jim and Andy derive a nominal Ge and InGaAs wavelength calibration using the May OCF calibration data in vacuum and at low TT. There are some small discrepancies between their results and those derived by Keith Peacock, but Jim believes these can probably be resolved by a more detailed comparison of data reduction techniques. Residual periodic signal in the InGaAs data is probably the result of time-depedent dark current drift. Every effort should be made during the July OCF run to characterize this drift over the short timescales of each of the monochrometer scan tests.

InGaAs SNR Analysis: Preliminary wavelength calibration of Ge and InGaAs detectors (written by Jim Bell)(retrieved 6/13/95)

Preliminary mapping of the Channel Number to spectral wavelength for the Ge and InGaAs detectors is presented, based on piecepart measurements.

InGaAs SNR Analysis and the detection and discriminability of mineral features(written by Jim Bell)(retrieved 5/20/95)

This analysis, presented at the NEAR MSI/NIS team meeting at APL, illustrates the effect of SNR on mineral feature discrimination. Jim concludes that for SNRs > 100, we should be able to detect and quantify at moderate accuracy the parameters of most of the spectral features we expect to see. If narrow absorption features are detected on Eros, we will need higher SNR values to assure ourselves of accurate band fitting. He warns that since we will not see perfect bands on Eros, nor will we see (most likely) bands as deep as those in pure lab minerals, his results represent best case, and we probably want to shoot for factors of two to five improvement in SNR (i.e, SNR > 200 to 500).

Extensive Calibration Analysis of CCD2 (including Dark vs. Exposure, Dark vs. Temperature, CCD Linearity, and Light Transfer Curve) (written by Mark Robinson)(retrieved 5/7/95)

This extensive analysis by Mark covers the basic observables from the piecepart CCD tests on the "new" (now final) MSI CCD, which we have been calling CCD2. It includes analyses of the dark current as a function of both exposure duration and temperature, CCD linearity (measured as a function of neutral density filter), and the light (photon) transfer curve. Conclusions include: 1) dark current contributions at nominal operating temperatures (i.e., -40° to -20° C) are very small (possibly negligible) over the entire range of exposures, 2) the detector response is linear to the degree measured by the neutral density filter test, and 3) the system has relatively low detector read noise (about 1.3 to 1.5 DN) and a scale factor of just under 100 e-/DN (92-99 e-/DN).

Example of Quantization Problem Mentioned in Veverka's Weekly Status Report (as "noise problem")(written by Mike Malin)(4/19/95)

This memo shows a representative MSI histogram and illustrates the problem recently seen in these data. Basically, not all 12 bits of the MSI histogram are occupied. The result are spikes in the histogram. The problem is manifested by all 3 lowest bits being occupied at low DN, some of the 3 lowest bits being occupied in the middle DN range, and none of the lowest 3 bits being occupied at high DNs. MOC experience with something similar was traced to a faulty analog-to-digital converter.

Scott Murchie's Analysis of the Scratch on the CCD (written by Scott Murchie)(4/11/95)

This report shows the visibility of the scratch and other blemishes on the new CCD detector in color and color ratio images. It includes color, color ratio, and high-pass filtered images, and line plots through and around the scratch. This report is a WWW version of Scott's 4/11/95 e-message plus the materials in retro.jhuapl.edu/project/near/SDC/MSI/scratch.

Discussion and Images of Scratch on New MSI CCD Detector (written by Mike Malin)(4/10/95)

This report shows the scratch and other blemishes on the new CCD detector. It discusses some of the concerns I have about finding these on the detector, and gives my position about replacing the detector.

NIS Calibration Report #4 (written by Scott Murchie)(2/23/95)

This report describes the spectral characteristics of the lamps used in piece-part testing, and the spectral response characteristics of the Ge detectors.

NIS Calibration Report #3 (written by Jim Bell)(2/22/95)

This report describes the linearity behavior of the Ge detectors at temperatures other than -26 C and in non-vacuum conditions. It draws three basic conclusions:

• At T=-20, -10, and +24 degrees (in vacuum and in air) and at gain=1, the flight Ge detectors all appear to exhibit excellent linear behavior over the range of incident flux sampled.
  
• At T=-20 and -10 and at gain=10, the limited amount of usable data from these tests indicate that the detectors are behaving linearly. However, many channels exhibit saturation, and so these tests need to be repeated over a better range of incident flux values. ALL of the gain=10 tests should be repeated after correcting the bias problem and devising a way to better vary the incident flux in order to confirm the tentative linearity results.
  
• There is not enough well-behaved test data available to fully assess the linearity of the detectors as a function of wavelength.

Description of Proposed Autoexposure Algorithm (written by Mike Caplinger and Mike Malin, 2/15/95)

This memorandum descibes and illustrates a proposed autoexposure algorithm for the MSI. The AE approach would acquire an underexposed test image, accumulate a 128 bin histogram by shifting each pixel value by 5 bits and accumulating a running count in each bin as the image is read out. A cumulative, high-to-low value sum would then be used to compute a percent (or number of pixels) to be "saturated," and the DN (determined from the bin number) at which this percent is achieved would be ratioed to the selected saturation value (nominally the full well of the detector, 4095 DN). This ratio is the number by which the test image exposure would be multiplied in order to properly expose the desired science image.

Optimized Shot Noise Companding for the MSI (written by Jeff Warren and Mike Malin, 2/15/95)

This memorandum descibes and illustrates a proposed companding approach to "compress" MSI data from 12-bits to 8-bits. Owing to counting statistics and the size of its detector's full-well, the MSI can only achieve 10-bits of noise-discriminable signal. Using a square-root companding table could reduce the MSI data by two bits without loss of information (i.e., there aren't strong reasons to encode noise). An additional two bits of "lossy" compression can be performed at the same time using a table that is linear across the signal-to-noise space.

NIS Ge Calibration Report #2 (Murchie Report #1)(written by Scott Murchie, 2/2/95)

This report describes Scott's analyses of dark current vs. temperature for the NIS Ge detectors. He shows that they vary significantly from detector to detector. He draws several conclusions important to the use of this focal plane as a science tool:

1. the two worst channels occur in the area of overlap with the InGaAs focal plane
2. the relatively bad "channel 30" occurs near 1.4 microns, where OH and/or H₂O absorptions might occur
3. alternative values of the first offset should be considered, since several of the detectors "zero'd out."

NIS Calibration Report #1 (written by Jim Bell)(1/25/95)

This report describes Jim's analysis of the Ge detector's sensitivity to absolute flux and its linearity, performed on data acquired at -26 deg C. Jim concludes:

1. At T=-26 degrees, the flight Ge detectors all appear to exhibit excellent linear behavior over the range of incident flux sampled.
   
2. The technique of using ND filters to regulate the incident flux is sound, however it is not optimal because many of the measurement situations do not allow the detectors to measure flux levels in the important range between half-full and saturation. These test results are not appropriate for determining whether or not the detectors are linear over the entire range of non-saturated DN values. At some point, we must perform tests that sample more finely the DN space (including the highest and lowest ranges).

Calibration Report #5 (1/22-XX/95)

This report is under construction.

Calibration Report #4 (1/10-15/95)

This report completes the initial analysis of calibration data acquired during for the "dirty" CCD. Included are: analyses of the -30 deg and -40 deg C test data, including dark current determinations, neutral density filter transmission, exposure response, and spectral curves (for -40 deg C only). The best "photon transfer curve" that could be made is included at the end of the report. Note: The photon transfer curves in these reports are suspect. Additional effort is underway to try to determine why they do not have the appropriate functional form. If anyone has a suggestion, please let Malin know. Also note that the reduction of the spectral data is very crude. Team members with specific interest and experience in reducing spectral data (in particular accounting for the spectral curve of the light source and the filters used during test) should take a crack at it. Tabular data on mean values at different wavelengths, etc. can be found in Reports #2 and #4, under "xxxT_picture_data.txt".

Calibration Report #3 (1/9/95)

This report finds the dark current accumulation rate (about 2-4 DN/sec at -20 deg C) and shows the "raw" spectral response curves for the "dirty" CCD (i.e., not corrected for either the lamp spectral curve nor the filter bandpasses, for which I don't have good data).

Calibration Report #2 (1/8/95)

This report describes some first-order calibration information I have derived from the Room Temperature (~20-24 deg C) and "High" Temperature (-20 deg C) calibrations performed on the "dirty" CCD. Among the important results are to show the effectiveness of the dark current correction, a derivation of the -20 deg dark current value (40 DN), and establishing some of the parameters necessary for determining the shot noise limitations on data encoding.

Calibration Report #1 (12/27/94)

This report describes the calibration image numbering scheme, raises a discussion of the image numbering scheme to be used during the mission, and describes results of the initial piece-part measurements on the MSI flight unit CCD.

malin@msss.com