Operational Oceanography Requirements

Le Traon et al. (2006) have defined the main priorities for altimeter missions in the context of the European GMES (Global Monitoring for Environment and Security) Marine Core Service. Their Tables 2.1 and 2.2 give the requirements for different applications of altimetry and characteristics of altimeter missions.

The main operational oceanography requirements for satellite altimetry can be summarized as follows:

1. Need to maintain a long time series of a high accuracy altimeter system (Jason series) to serve a reference mission and for climate applications. It requires one class A altimeter with an overlap between successive missions of at least 6 months.

2. The main requirement for medium to high resolution altimetry would be to fly three class B altimeters in addition to the Jason series (class A). Most operational oceanography applications (e.g. marine security, pollution monitoring) require high resolution surface currents that cannot be adequately reproduced without a high resolution altimeter system. Recent studies (e.g. Pascual et al. 2006) show

Table 2.1 User requirements for different applications of altimetry

Application area Accuracya Spatial resolution Revisit time Priority

Table 2.1 User requirements for different applications of altimetry

Application area Accuracya Spatial resolution Revisit time Priority

(cm)

(km)

(days)

1.

Climate applications and 1

300-500

10-20

High

reference mission

2.

Ocean nowcasting/forecasting for 3

50-100

7-15

High

mesoscale applications

3.

Coastal/local 3

10

1

Lowb

a For the given resolution

b Limited by feasibility

Table 2.2 Altimeter mission characteristics

Class Orbit

Mission characteristics

Revisit interval

Track separation at

(days)

the equator (km)

A Non-sun

High accuracy for climate

10-20

150-300

synchronous

applications and to ref-

erence other missions

B Polar

Medium-class accuracy

20-35

80-150

that, at least three, but preferably four, altimeter missions are needed for monitoring the mesoscale circulation. This is particularly needed for real time nowcast-ing and forecasting. Pascual et al. (2009) showed that four altimeters in real time provide similar results as two altimeters in delayed mode. Such a scenario would also provide an improved operational reliability. Moreover, it would enhance the spatial and temporal sampling for monitoring and forecasting significant wave height.

In parallel, there is a need to develop and test innovative instrumentation (e.g. wide swath altimetry with the NASA SWOT mission) to better answer existing and future operational oceanography requirements for high to very high resolution (e.g. mesoscale/submesoscale and coastal dynamics). There is also a need to improve nadir altimetry technology (resolution, noise) and to develop smaller and cheaper instruments that could be embarked on a constellation of small satellites. The use of the Ka band (35 Ghz) allows, in particular, a major reduction in the size and weight of the altimeter. It will be tested for the first time with the CNES/ISRO SARAL satellite scheduled for launch in late 2011.

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