| Author | Message | ||
     Howard Mark (hlmark) Senior Member Username: hlmark Post Number: 137 Registered: 9-2001 |
Tony - "Remission" is a good overall term to cover any measurement where the light comes back to the instrument on the same side of the sample. Nevertheless, reflection, transflection and interaction are, as I described in the earlier posting, different ways of making a measurement, and need labels that distinguish between them. Also, "reflection", especially, is a term used far beyond the boundaries of NIR, or of spectrsocopy, or even of science. We'll be lucky to get consistent usage even within our own small sphere of interest, and we're certainly not going to change the whole world to use our terminology; at the very least, we have to be willing to adapt to outside usages. Your own example of using "Herschel" versus "short-wavlength" is an indication to me, at least, of the kind of problems we're going to have in just trying to get consistency of usage among ourselves. \o/ /_\ | ||
| Tony Davies (td) Moderator Username: td Post Number: 166 Registered: 1-2001 |
Dear Don, Howard, Kerry, David and ..., Now that I have no direct connection to JNIRS or NIR news I am free to give my own opinion. I would like the NIR community to give their support to the use of "remission" then we could forget all the past confusion. If ICNIRS (CNIRS as well but I think this has to be an international agreement) would like to give a lead then the Editors of JNIRS and NIR news could and should encourage its use but I do not think that publications should actually try to force the Editor's view. In the first issue of JNIRS there is a paper by Anthony Bonanno and Peter Griffiths "Short-wave near infrared spectra of organic liquids". I have a strong dislike of the term "Short-wave" added to NIR and tried to get the get the authors to use the term "Herschel NIR" (which I had proposed in a letter to the Editor of Applied Spectroscopy) but Peter was not keen. He did agree to change the paper "If you insist". I decided that this would be a misuse of my editorial power (but I still hope that one day we will agree to honour the discoverer of the NIR region. [Well actually he discovered ALL energy outside visible although he failed to detect UV]). Sorry that�s a digression but I just wanted to emphasise the point that in my view editors' powers should be limited. I was going to add something about not being concerned about software providers � but perhaps I should refrain! Best wishes, Tony | ||
| Howard Mark (hlmark) Senior Member Username: hlmark Post Number: 136 Registered: 9-2001 |
From the scientific point of view, it's of course better to have unambiguous definitions for terminology. If we're going to ask the various journals to follow the terminology we decide on, then we will have to agree on what those definitions should be, and speak with one voice, before approaching any journal publishers. I think this would be a good activity for the CNIRS to undertake; it certainly fits in with the mission statement. Possible objections might come from software providers (both the instrument manufacturers provide software with their hardware, and the various third-party software vendors) who have the terms hard-coded into their products and would want to avoid confusing their customers by changing terminology. In order to overcome that, it would be benficial to also include them in the standarization process. There's also the possibility of disputes arising from this, however, as happened in the early days of the ASTM commitee. With all that, if history is any guide, there will always be some confusion, because of the existence of historical usages of the various other terms, and people referring to them (especially newcomers to the field) will not be aware of the standard usage. \o/ /_\ | ||
| kerry walsh (walshk) New member Username: walshk Post Number: 3 Registered: 2-2007 |
Don - I see you started this thread in Umea...a case of a little too much reflectance through your hotel window and too little sleep? But as the topic has strayed to interactance....could I add .... Foss/NIRSystems has marketed an 'interactance probe' (concentric illumination and detection fibres). However, I find the term too vague in wider use and prefer to use the term 'partial transmission' followed by a qualification of the optical geometry employed. Does this seem fair? re your call for consistent terminology...this is sensible, although as you say its usually obvious what is meant in context. So I suspect its a case of the activation energy required to effect a change ( when will you get around to going metric?) Kerry | ||
| Donald J Dahm (djdahm) Intermediate Member Username: djdahm Post Number: 20 Registered: 2-2007 |
Howard raised the issue of whether the technique should be called "Interactance", or "Interaction". When I "goggle" the word "interactance", the only supplier I seem to come up with is Foss, but there doesn't seem to be anything in their product literature to suggest that the term is copyrighted. The term interactance seems to be pretty widely used in the literature to describe the experimental arrangement that was described in the paper that started me on this "pretend tirade". (The word offended was a hyperbole.) The best compilation of definitions that I have is from the Handbook of Vibrational Spectroscopy". The author, John Bertie, has been very responsive our suggestions, though he has not adopted all of them. This is the source that Howard quoted. There is general agreement that the word "transmission" refers to the mode of collection and that "transmittance" refers to the specific measurement of the fraction of light transmitted (what we usually symbolize as "T") and the fraction is of course multiplied by 100 if it is labeled "percent transmission". If you go back into the NIR News achieves, you will see that I prefer the terms remission and transmission. Tony seemed to be encouraging a move in that direction in the NIR Publications materials before he retired. For the remission case the terms "promoted" by the Society for Applied Spectroscopy are the analogous use of "reflection" and "reflectance, though they have no quarrel with using the word "remission". There is a glossary of terms in each January issue of Applied Spectroscopy" that explains their current view. Interestingly, until 2007 they ignored definitions related to scattering samples. (Yes, I was instrumental in getting them to add it.) The physics community tends to use the word reflection to refer to the (angle of incidence equals the angle of reflection) and "reflectance" when the dispersed remission is included. The NIR community has traditionally used the words in this way as well. My question is this: Is the NIR community ready to ask our Journal and Newsletter editors to adopt one of these conventions and enforce it, or is it preferable to continue to use the words with some ambiguity. It is generally not hard to figure out what is meant by the context. | ||
| Howard Mark (hlmark) Senior Member Username: hlmark Post Number: 105 Registered: 9-2001 |
David - I DO sometimes get "offended" - - - when people use certain terms and apply them to me!!! Fortunately, people on this discussion group are genteel and don't do that!! VenkyNIR - ATR is rarely. if ever, used in NIR, although it's common in mid-IR. The reason is that with ATR, the pathlength in the sample, which is on the ATR plate, is proportional to the wavelength. Therefore the pathlength through the sample is short in the NIR. The combination of short pathlength and weak sample absorbtivity makes it difficult to see the sample absorbances. There was once an instrument on the market that was designed to measure using ATR in the NIR region but it was withdrawn, probably due to lack of sales. I'm afraid I don't understand the thrust of your questions about mode or about gap length? \o/ /_\ | ||
| venkatarman (venkynir) Senior Member Username: venkynir Post Number: 42 Registered: 3-2004 |
Thanks for HowardMark, for such a beautiful Explantion .Can you say some thing about ATR and Total refelection . How it will helpful to NIRS measurement ? How to select the mode as Instrumentation point view? More over in the case of reflectance the gap length is minimal in NIR instruement why ? please answer Howadmark. venkynir | ||
| David Russell (russell) Senior Member Username: russell Post Number: 34 Registered: 2-2001 |
To reinforce Howard's response, the term transflectance was used a lot in connection with liquids analysis where a reflector was used in conjunction with either a sample cell or a fiber optic probe to permit the source and collection optics to be in a single subassembly. This practice introduced it's own set of problems which were ultimately eliminated through the design of appropriate transmission sample accessories. I tend not to be "offended" by the misuse of terms, but agree that the use of the term transflectance in the referenced application is incorrect. | ||
| Howard Mark (hlmark) Senior Member Username: hlmark Post Number: 103 Registered: 9-2001 |
Don - Karl was the person who coined "interactance" (or maybe we should say "interaction" to satisfy the purists among us!) as the descriptor for a measurement where the surface was illuminated at one point and the light remitted from a distant, non-illuminated point was measured. There was no consideration given to whether there was any sort of light shield in between, or what the distance from the illuminated region was. My interpretation is that "interactance" covers both cases. The reason for the new term was to distinguish this measurement mode from "reflection", where the regions of illumination and measurement are the same, or at least overlapping. "Transflection" is a completely different measurement mode. The term is a melding of "transmission" and "reflection". It was created to describe the situation where a clear liquid was to be measured, so that the light through the sample was in fact transmitted through the sample itself, but the available instrumentation was only able to measure in a reflection mode (as essentially all the early instruments were limited to that measurement mode). So the liquid cells were designed with a reflector in the back, behind the sample, to allow the incoming light to be transmitted through the sample twice, while the instrument didn't have to be reconfigured to measure these clear (or partially diffusing) samples. The distinction of transflection from pure reflection is that for transflectance the sample is not the source of the remisssion, the reflector behind the sample does that, while in reflection the sample itself is also the source of the remission. So while I don't feel "offended" by the usage described, it is not in keeping with the historic use of the various terms. The only place I know where it has been written down is in the glossary in volume 5 of Peter Griffith's and John Chalmer's "Handbook of Vibrational Spectroscopy". There is no listing for "interactance" or "interaction" having meaning as an optical measurement mode, but the terms "Reflection" and "Transflection" are described thus: Reflection - The process by which radiation is reflected by a sample. For non-scattering samples the term means �Fresnel reflection� (see above) or �specular reflection� (see below); for scattering samples the term includes �regular reflection� (see below) and �volume reflection� (see below) or �diffuse reflection� (see above). Transflectance - The ratio of the spectral intensity of the transflected beam to the spectral intensity of the incident beam in a transflection experiment. �Transflectance� has also been used to mean �transflection� (see below), and this usage is strongly discouraged. Transflection - A term that has become common in recent years for reflection absorption at "near-normal incidence" when the thickness of the absorbing medium is large enough to yield an interpretable spectrum. The substrate is usually a mirror for mid-infraredmeasurements and a ceramic disk for near-infrared measurements. The angle of incidence is typically between 0� and 45�. Transflection is widely used in IR microscopy and is particularly convenient for measuring transmission-like spectra in a near-infrared instrument configured for diffuse reflection measurements by mounting the sample on a non-absorbing diffusely reflecting substrate. \o/ /_\ | ||
| Donald J Dahm (djdahm) Member Username: djdahm Post Number: 11 Registered: 2-2007 |
I'm at NIR-2007. One of the speakers called "transflectance" a geometry where light was injected into a piece of meat, and detected from the same surface on the other side of a light shield placed on the surface. This reduces the remission detected from the near surface, as well as any specular reflectance. In the old days" at NIRSystems, we would have called this "interactance". My question is: Does this use of the term "transflectance", when the sample is infinitely thick offend anybody else besides me? |