Sentinel-3 OLCI vs. MODIS/VIIRS – the overall tally


Based on my initial look at the Sentinel-3 data (see part 1, part 2 and part 3 for the details) here some comparitive assessments relative to the existing MODIS/VIIRS systems. As indicated in the title this is for OLCI, i.e. visible light and NIR only since the evaluation of SLSTR is incomplete due to errors in the geolocation data.

This is preliminary of course – based on the currently available data and my limited experience with that data. It covers a number of different fields i consider relevant for choosing a satellite data source. Which of the criteria listed are more important and which less of course depends on the use case.

# Topic Sentinel-3 OLCI MODIS VIIRS
1 Data point quality + o o
2 Data depth + o o
3 Resolution o o
4 Image archive ++ o
5 Revisit frequency -/o + ++
6 Temporal Coverage early Morning Morning + Afternoon Afternoon
7 Spatial Coverage + +
8 Data packaging/usability + + o
9 Ease of data access o + +
10 Higher level products + +
11 License + ++ ++

More detailed notes about the individual categories:

  1. Data point quality refers to the quality of the individual data points (i.e. pixels) in the images, i.e. noise levels and radiometric accuracy. In terms of noise OLCI likely has an advantage over the >15 year old MODIS although as explained this will not really make much practical difference. Also both MODIS and VIIRS show a banding effect in images due to the way their scan system works which does not occur with OLCI.
  2. Data depth means the scope of information available for every point. Sentinel-3 OLCI leads here due to the additional bands. The narrow bands with somewhat suboptimal position w.r.t. visulization purposes reduce this but still a lead compared to MODIS and VIIRS which are not ideal either.
  3. Resolution – as discussed this is more or less a tie between OLCI and MODIS. VIIRS is clearly behind.
  4. Image archive refers to the size of the archive of past recordings that is available for use. Here MODIS has a huge lead of course.
  5. Revisit frequency means how frequently images are recorded at a given location. Apparently even with two satellites OLCI will not be better than MODIS with just a single satellite here. VIIRS leads with full daily coverage with even a single satellite.
  6. Temporal Coverage – is not really a rating category although you could say MODIS is the most versatile here with both morning and afternoon satellites. Since for Sentinel-3 the second satellite will cover the same time slot this will not change with Sentinel-3B.
  7. Spatial Coverage – this refers to what part of the Earth surface can be and is practically covered. Due to lack of south pole coverage Sentinel-3 is behind here. You also need to consider the relatively tight sun elevation cutoff of 10 degrees – limiting spatial or temporal coverage depending on how you look at it.
  8. Data packaging/usability – Both Sentinel-3 and MODIS have pros and cons here, no clear winner. VIIRS is somewhat behind due to relatively poor documentation and complex packaging and processing levels.
  9. Ease of data access – The Sentinel data access is – due to the mandatory use of the API and the need to register (except for the current so called pre-operation phase) – less convenient than the others.
  10. Higher level products – Currently Sentinel-3 data is only available as Level 1 data while the other sensors offer a broad selection of higher level products.
  11. License – all are open data but the vague attribution requirements for Sentinel-3 data are a possible issue for some applications.

And here for wrapping up three more views from Sentinel-3 OLCI – you can use these under CC-BY-SA conditions if you want:

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