VNREDSat: turning optical images into evidence

VNREDSat-1 was developed for Vietnam’s natural-resource, environmental and disaster-monitoring needs through VAST’s partnership with France’s EADS Astrium. It launched on a Vega rocket in May 2013, followed by a September handover for Vietnamese operation. Its contribution differs from VINASAT: rather than primarily relaying customers’ messages, this spacecraft measures reflected light from Earth and sends the observations to receiving and processing facilities. Its archive card uses the catalog name VNRedSat-1A.

The project connected spacecraft control with image reception, archiving and analysis. Those ground responsibilities are part of national observing capability. VAST’s earlier annual report also documents planning for a follow-on called VNREDSat-1B with a Belgian partner. A proposed follow-on belongs in the family’s development history, but that planning record does not demonstrate that the proposed spacecraft was built, launched or delivered a stream of images.

VNREDSat-1 provides finer spatial sampling in its broad panchromatic — open definition channel than in its multispectral — open definition channels: the published values are 2.5 metres and 10 metres respectively. Multiple spectral bands can help distinguish surface properties, while finer spatial detail helps locate boundaries and small features. Neither advantage makes the other redundant. Image interpretation depends on both what wavelengths are measured and how much ground each sample represents.

For a simplified example, a square 10-metre ground sample covers 100 square metres; a 2.5-metre square covers 6.25 square metres. Sixteen smaller squares fit within the larger one. This area comparison does not mean sixteen times more spectral information or guaranteed identification of every object. Clouds, shadows, contrast, viewing angle and processing still affect what the scene can reveal. A pixel size is a sampling measure, not a complete statement of interpretive accuracy.

Spatial sampling has two dimensions

Vietnam’s National Remote Sensing Department reported an interruption beginning in late 2023 and a return to operation on April 30, 2025. That is a dated recovery milestone, not a promise of uninterrupted future coverage. The same agency’s discussion of clouds makes another useful distinction: an acquired scene and a scene suitable for a particular analysis are not necessarily the same. Researchers should preserve quality information when building a time series.

Suppose a flood study has clear images before and after an event but cloud obscures the peak. The record can show changes between the available dates, yet it cannot directly establish the maximum flooded area. Other observations and field reports may fill part of that gap. VNREDSat’s value therefore includes both locally controlled acquisition and the expertise to explain the evidence’s limits, helping users avoid turning an incomplete image archive into an overconfident account of events.