Figure VI. Model values for current spatial density Spatial density(number/km) 10 A≥1mm B≥1cm 104c≥10cm A 105 10 B 10 108 10 02004006 800100012001400160018002000 Altitude( km) Sources: NASA (ORDEM96): DERA (IDES): ESA(MASTER): CNUCE (SDM): and NAZARENKO