Table 2.
Required accuracies and stabilities of satellite instruments to meet requirements of Table 1. The instrument column indicates the type of instrument used to make the measurement
| Instrument | Accuracy | Stability (per decade) | |
|---|---|---|---|
| SOLAR IRRADIANCE, EARTH RADIATION BUDGET, AND CLOUD VARIABLES | |||
| Solar irradiance | Radiometer | 1.5 W / m2 | 0.3 W / m2 |
| Surface albedo | Vis radiometer | 5 % | 1 % |
| Downward longwave flux: Surface | IR spectrometer and Vis / IR radiometer | See tropospheric temperature, water-vapor,cloud base height, and cloud cover | See tropospheric temperature, water-vapor, cloud base height, and cloud cover |
| Downward shortwave radiation: Surface | Broad band solar and Vis/IR radiometer | See net solar radiation: TOA, cloud particle effective size, cloud optical depth, cloud top height, and water-vapor | See net solar radiation: TOA, cloud particle effective size, cloud optical depth, cloud top height, and water-vapor |
| Net solar radiation: Top of atmosphere | Broad band solar | 1 W / m2 | 0.3 W / m2 |
| Outgoing longwave radiation: Top of atmosphere | Broad band IR | 1 W / m2 | 0.2 W / m2 |
| Cloud base height | Vis / IR radiometer | 1 K | 0.2 K |
| Cloud cover (Fraction of sky covered) | Vis / IR radiometer | See cloud optical thickness and cloud to temperature | See cloud optical thickness and cloud to temperature |
| Cloud particle size distribution | Vis / IR radiometer | TBD* | TBD* |
| Cloud effective particle size | Vis / IR radiometer | 3.7 μm: Water, 5 %; Ice, 10 % 1.6 μm: Water, 2.5 %; Ice, 5 % |
3.7 μm: Water, 1 %; Ice, 2 % 1.6 μm: Water, 0.5 %; Ice, 1 % |
| Cloud ice water path | Vis / IR radiometer | TBD* | TBD* |
| Cloud liquid water path | Microwave and Vis / IR radiometer | Microwave: 0.3 K Vis/IR: see cloud optical thickness and cloud top height | Microwave: 0.1 K Vis/IR: see cloud optical thickness and cloud top height |
| Cloud optical thickness | Vis radiometer | 5 % | 1 % |
| Cloud top height | IR radiometer | 1 K | 0.2 K |
| Cloud top pressure | IR radiometer | 1 K | 0.2 K |
| Cloud top temperature | IR radiometer | 1 K | 0.2 K |
| Spectrally resolved thermal radiance | IR spectroradiometer | 0.1 K | 0.04 K |
| ATMOSPHERIC VARIABLES | |||
| Temperature | |||
| Troposphere | MW or IR radiometeer | 0.5 K | 0.04 K |
| Stratosphere | MW or IR radiometer | 1 K | 0.08 K |
| Water vapor | MW radiometer | 1.0 K | 0.08 K |
| IR radiometer | 1.0 K | 0.03 K | |
| Ozone | |||
| Total column | UV/VIS spectrometer | 2 % (1 independent), 1 % (1 dependent) | 0.2 % |
| Stratosphere | UV/VIS spectrometer | 3 % | 0.6 % |
| Troposphere | UV/VIS spectrometer | 3 % | 0.1 % |
| Aerosols | VIS polarimeter | Radiometric: 3 % Polarimetric: 0.5 % |
Radiometric: 1.5 % Polarimetric: 0.25 % |
| Precipitation | MW radiometer | 1.25 K | 0.03 K |
| Carbon dioxide | IR radiometer | 3 % | Forcing: 1 %; Sources/sinks: 0.25 % |
| SURFACE VARIABLES | |||
| Ocean color | VIS radiometer | 5 % | 1 % |
| Sea surface temperature | IR radiometer | 0.1 K | 0.01 K |
| MW radiometer | 0.03 K | 0.01 K | |
| Sea ice area | VIS radiometer | 12 % | 10 % |
| Snow cover | VIS radiometer | 12 % | 10 % |
| Vegetation | VIS radiometer | 2 % | 0.80 % |
*
To be determined