Does DA/DH refers to ceiling?

Question

If airport is reporting FEW001 or SCT001 and RVR is above 600m, does it means that there will be no LVO because ceiling is defined as more than 4/8 and DA/DH will be more than 100ft because DA/DH is defined in the name of ceiling. Or what if some of the SCT001 clouds will get over missed approach point, which is exatly at DA/DH, when pilots have to make decision. So they might not see the RWY at DH200ft, because of SCT001.

Answer 1

If I am understanding your question correctly:

An LVO is Low Visibility Operations which is defined by the FAA in AIM 2-3-4 and 4-3-19 as well as Advisory Circular 120-57a & ICAO OPS Low Visibility Operations (LVO)

Low visibility operations are those that occur when the runway visible range (RVR) is below 1200 feet (360m).

So, your RVR above 600m would not indicate the need for LVO.

A Ceiling is defined by the FAA

Ceiling means the height above the earth’s surface of the lowest layer of clouds or obscuring phenomena that is reported as “broken,” “overcast,” or “obscuration,” and not classified as “thin” or “partial.”

And, Broken (BKN) cloud layer is defined in AIM 7-1-31

9. Sky Condition.
The sky condition as reported in METAR represents a significant change from the way sky condition is currently reported. In METAR, sky condition is reported in the format:

Amount/Height/(Type) or Indefinite Ceiling/Height

(a) Amount. The amount of sky cover is reported in eighths of sky cover, using the contractions:

SKC clear (no clouds)

FEW >0 to 2/8

SCT scattered (3/8s to 4/8s of clouds)

BKN broken (5/8s to 7/8s of clouds)

OVC overcast (8/8s clouds)

CB Cumulonimbus when present

TCU Towering cumulus when present

Note 1: “SKC” will be reported at manual stations. “CLR” will be used at automated stations when no clouds below 12,000 feet are reported.

Note 2: A ceiling layer is not designated in the METAR code. For aviation purposes, the ceiling is the lowest broken or overcast layer, or vertical visibility into an obscuration. Also there is no provision for reporting thin layers in the METAR code. When clouds are thin, that layer must be reported as if it were opaque.

So, the cloud layers you described as FEW001 or SCT001 would not be considered a ceiling. And, they would not be considered IMC.

More insight on what can be done at the MAP can be gathered from this question:
Missed Approach below DA/DH

Answer 2

You’re right if clouds are less than 5/8 they do not construe a ceiling and does not satisfy the ceiling being below DA/DH.

DA/DH is as the name applies is the decision point for the pilot. If pilot believes a safe landing is not possible at DA then she/he need to do a missed approach. That’s is not limited to clouds which is less than 4/8 but also can be (for the lack of imagination) say a burning car’s smoke which is precluding the visual with the runway. There are 3 requirement to meet before you can descent below DA/MDA per 14 CFR § 91.175:

(1) The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers, and for operations conducted under part 121 or part 135 unless that descent rate will allow touchdown to occur within the touchdown zone of the runway of intended landing;

(2) The flight visibility is not less than the visibility prescribed in the standard instrument approach being used; and

(3) Except for a Category II or Category III approach where any necessary visual reference requirements are specified by the Administrator, at least one of the runway environments is distinctly visible and identifiable to the pilot”

First paragraph addresses your question. You need to be in a continuous safe position all the way down to the runway. So if something is blocking your vision to the runway then you need to start a missed approach.

On the other hand, if you’re flying Part 91, you can shoot the approach even if the weather is below minimums (e.g. more than 4/8 clouds reported below DA/MDA). In that case, if you satisfy the 3 requirements above at the DA/MDA, then you can continue with the landing. Part 121 and 135 don’t even allow to shoot the approach in the first place, in such a case.